The 225 – 250 temps you’re most likely referring to are best for fatty, tough cuts with lots of connective tissue like butts, briskets, and ribs. Butts and brisket are best served at internal temps of at least 185 (I've never measured the temperature of ribs). It takes a long time to break down those tissues and render out much of the fat. It’s a process that really can’t be hurried with a higher cooking temperature.
Higher temps (325) are best for leaner cuts of meat such as standing rib roasts and whole loins. They have much less fat content and will be too dry for most people when cooked above medium doneness. These cuts can be cooked satisfactorily at the lower temperature but a higher temp helps sear the meat and form a tasty crust.
Like the higher priced cuts of meat, poultry can also be done at a lower temperature but the skin will be tough, rubbery and thoroughly unappealing. Cooking at temps above 300 will make the skin much crisper.
These temperatures are just general rules of thumb. Individual preferences will vary, of course, but that comes with personal tastes and experiences.
The lower grate on one of my bullets is around 12-15 degrees cooler than the top. Not a big deal in my book. When cooking similar meats, the smaller hunk goes on the bottom grate to even out the cooking times. I don’t measure my dome temperature, but I’d guess there's at least a 30-degree difference between the dome and the lower grate on yours.
Sounds like you've had good success with the temps and methods you've been doing so stick with it. As the old saying goes, "Dance with what brung ya."
