1.6rc1 seems to be out now in the Arch repos, although I haven't noticed any differences from 1.5.31.
Intel GMA965 here, though, just updated to xf86-video-intel 2.21.9.
It's probably your video drivers, you said you compiled them yourself. Did you install them after you played BL the last time?
EDIT: I actually think I gained about 3-4fps in minimum shaders now, hm.