I'm always trying new grain bills for my IPAs, but my favorite so far has been 9.5# 2-row, 1# Vienna, and 0.5# Crystal 60. That's with ~80% mash efficiency though and only ~5.7% abv. So a very generalized answer to your question would probably be anywhere between 9-15#, plus your specialty grain, but depending on your efficiency to hit the OG you're after.