Jim,
I didn't draw a conclusion.
Yes, there are numerous variables that together affect outcome.
Low temps allows the meat's surface to dry rather slowly--especially in a cooker with a waterpan, but it is the case irrespective of this. Evaporative pressure is less but because there is evaporation the meat's surface stays cooler than one might expect and the meat is gently cooked. This method is offers a larger 'done' window usually. Think of a butt.
At high temps (375, 400 or more) the surface of the meat browns (caramelizes) and the evaporative pressure is significantly greater. There is significantly more moisture loss and the outside portions of the roast are more done than the inside (if pulled early--think of a tenderloin roast cooked to med-rare--or can become overdone and dry if the roast contains less fat/connective tissue--think of a large cut from the round cooked at high heat. The 'done' window is much narrower.
In conventional roasting, i.e., roasting in an oven, the usual cook temp is moderate--in between the low and the high, or about 350. Sometimes the cook is started at high heat to foster caramelization of the meat's exterior but this is a personal preference thing. The moderate temps during these cooks offer a compromise between high temp cooking and low and works well in many cases. There are personal--not mandatory--exceptions to this, like choosing to cook a tenderloin or rib roast at 200 after an initial sear so that the result is more evenly done, or choosing to roast a pork tenderloin at 500 to obtain significant browning but a short cook time (pulling the meat at ~135-140 internal so as not to overcook).
So, where might this leave us in terms of typical Q meats? Well, the first thing to remember is that in barbecue we are cooking the meat past conventional 'done' (in terms of internal temp) to 'done' meaning tender. Though low/slow is valid for all meats we barbecue I think that 'low/slow' needs a better definition in most cases. For conventional (read: supermarket) briskets, chucks, butts and spares I think a temp of ~275 grate
is low/slow. Most butts can support lower temps than this (which can be handy if one requires a longer cook for scheduling (or sleep!) purposes), as can spares usually, but with briskets it's a crap shoot. Even though at the lower temps of 200-230 say, the cook is gentle and the evaporative pressure minimized, many briskets simply do not have the internal renderable fat and connective tissue to warrant temps this low--in my opinion--and suffer as a result.
Sidebar: At temps above 120, myosin begins to coagulate. As temps rise and coagulation continues, moisture is forced out from between the myosin molecules as they bond together. As temps pass 140 more proteins coagulate and more moisture is squeezed and the meat feels significantly firmer asa result. Soon, the collagen in the connective tissue starts to denature and the connective tissue shrinks. This shrinkage puts pressure on the moisture in the interior portions of the muscle cells that are surrounded by the shrinking connective tissue. As temps rise further the meat gets stiffer and dryer. Then, at temps ~160, collagen in the connective tissue starts to dissolve into gelatin. As cooking continues, the connective tissue that held the muscle fibers together softens substantially. Now the muscle fibers that the connective tissue held together when it was intact start to be able to be easily pushed apart. When this process is completed and the connective tissue is soft and gelatinous, we have what we know as 'fork tender'. Much moisture has been lost (due to being forced out by the denaturing of the proteins and evaporation) but some remains trapped. Moreover, it is the breaking down of the connective tissue into gelatin and the rendering of internal soft fat pockets that gives us the soft, meltingly tender mouthfeel of good barbecue.
Though all meats have connective tissue that hold the muscle fibers together internal fat levels vary. In some cuts--say a thick butt or relatively thin spares--there is enough renderable fat along with connective tissue that allows the cook a wider range of cook temp possibilities. For other cuts--say supermarket briskets and babybacks--there is relatively less and this narrows the range, imo. However gentle cooking at very low temps might be, I think that one opens the door to excessive moisture and mouthfeel loss in many cases, i.e., the cook time is too long for the amount of internal renderable fat and the longer cook time allows for increased evaporation of moisture being forced from between the protein molecules. This is where I think one needs to weigh several of the variables noted above to determine best cooking temp. I see significant differences in a standard supermarket brisket cooked at 210, say, and a Prime brisket cooked at the same temp, or a standard slab of ribs from the market and one from a fattier pastured pig. The hindquarter from the Duroc cross we raised was significantly fattier--and contained much more finely striated fat--than a supermarket fresh ham one normally gets. This allowed me to braise it very slowly (in mojo) till done, cool it, cut it into small, bite-sized pieces, then reheat it in reduced braising liquid for serving and not worry that it would end up dry--not something I could do as well with a supermarket fresh ham. Imo, I would have had to undercook a conventional fresh ham, then cool it and cut it, and reheat gently and very carefully so as not to allow it to dry out.
I think, again for conventional supermarket cuts, the upper 200s offer a good compromise in terms of cook speed--slow enough to offer rendering/tissue breakdown, fast enough to disallow excessive evaporative loss. And, again, the cuts with the most of both offer the cook a wider range of temp possibilities. Temps can be pushed higher, if one wishes, by the use of foil which offers both a heat shield and, if closed around the cut, braising possibilities. I do not care for butts that are high-heat cooked with foil but I do like brisket done this way. Both can be cooked successfully at ~275 grate without the use of foil during cooking but this is a personal preference thing. It should be noted that one needs to consider bark components, especially sugars, when determining cook temp and whether to foil. Sugars caramelize at 335+ and burn at 350+. Though evaporation at the surface will keep it cooler for a time there is a line; cross it and the bark burns. Either be very careful, cook at temps below 335 (I like ~310-325 for brisket if using foil even though I rarely use sugar in the rub), or plan on using foil as a shield.
