All Voodoo2s have 4MB of framebuffer memory. There are two texture mapping units that have 2MB each (2x2 per tmu + 4 framebuffer = 8MB total) or 4MB each (2x4+4 = 12MB total). The memory upgrade is just doubling the TMU memory. I think any different RAM part numbers are just chips from different manufacturers that are functionally equivalent. I haven't checked my card but what's the worst that could happen?