BTW, I had a lack of 2D acceleration in my unsupported radeon graphics card (Kaveri APU R7), but my desktop wasn't so slow, only 2D games were slow (for example, supertux). Try to start X with it's default configuration (if you didn't allready, that means remove your manual configuration). Also that may be a GNOME bug, does that happen if you start any other desktop?
BTW, I forgot to tell what exactly "allowapperture" does:
http://man.openbsd.org/xf86