I have both 1.5-8 and 1-5 XTRII, used both in 3gun matches. I'm very happy with the pair, the 8x has come in handy shooting sage rats (1/3 size of a prairie dog) out to 200yds.
I haven't dialed beyond 6x in a match yet, but the extra magnification allows me to use the rifle in multiple roles. Personally I don't mind having the exposed knobs, not a huge deal with the zero stop. Love it even more after a 3gunstuff cat tail install.