I can remember when I started with the wsm just a couple of years ago freaking out when I cooked a butt and the temp climbed to 250! 220-235 was THE target. A friend cooks butts in an open pit for 12 hours. You and I know he is getting higher temps. After reading these resonses, my guess is we can cook at up to 300, maybe 325. IF you want to. You probably would have to eliminate sugar from the rub. My friend uses only salt and pepper. I would also assume that you would sacrifice some smoke flavor by speeding up the process. Butts are probably the most forgiving meat and will do well if cooked 12-24 hours given that you reach a reasonable internal temp and fork tender.
On ribs, I have dried them out when cooking them at 225 for 5 or 6 hours. So I have retreated to Raichlen's method in How To Grill and cook at 300-325 for 3.5 t0 4 hours with about 45 min in foil included. With the large surface area, ribs do not seem to lose anything by cooking quicker. My best results seem to come from the top rack if I don't rotate.
Briskets-I'm still learning these too. My early ones were cooked at 230 and foiled at 165. I loved em but truthfully they were more like pot roast. I started using foil at higher temps and then no foil. The flavor seems best with no foil but lacks a little of the moisture of foiled cooks. I have not tried to cook a brisket in 5 hours as Myron Mixon has. If Jim Minion cooks a brisket at 325...then it can be done. I would do anything to get the extra fat in a point rendered. Separating the point and leaving it on for a few hours seems to help some but, I still find myself using the point in soup or chili... Cooking hotter and quicker may be ok for a flat but I gotta think the point needs more time to render.
M D cooking one in 6 hours would be quicker than any I've cooked. Since you were on a kettle were you cooking at higher temps?