I really want to try a gain-twist 22-250 one of these days. Starting at around 1 in 15 or so, and gaining to about 1 in 9 28 inches later. In a 22-250 AI, I believe this should offer similar life to a 12 or 14" 22-250, yet still be able to stabilize heavy bullets. Gain twists often buy you a few more FPS, too.
From what I've heard of fast twist 22-250 (non-gain), the throad wears out very quicky. Within a thousand rounds or so, it's so rough that fouling becomes a major issue, and starts damaging the thing jackets of most match bullets to the point where they start coming apart in flight