this could depend on your rub as well...
read my old thread on salt and ratios of seasoning in rub...
http://www.bbq-brethren.com/forum/showthread.php?t=57130&highlight=salt+funk+rub
I used to notice what you were talking about when I had an aggressive rub (one with more than 4-5 powdered spices)
when i added a tri level to the act the 275 was kicked up drastically and the flavor from the same rub was driven into the meat more...
My pork rubs are high sugar, so your correct, they dont take to high heat. When I have cooked brisket at 300+ then thinner parts of the flat came out tough and in general I didnt like the results. 250-275 works great for everything I smoke, plus that is the temp my Party like to cruise at. I dont consider that high heat smoking, but I know alot of people do. Im just happy the days of stressing if the smoker got over 230 are over.