On G92 cards there was a strong (but not perfect) correlation between used memory chips and BIOS version, which you can ask the seller to take a picture / screenshot of.
I would not split. Choosing the right CPU stepping and mainboard chipset is also part of the game. Same applied to unlockable AM2+/AM3 chips and no one ever complained.
I've seen guys like Spcial (from hardwareluxx forums) and @stunned_guy run 32M as high as 700MHz with DDR2.
So there might be higher suicide screens that haven't been widely published.
No M0 so doesn't count
I'm amazed by how no one has yet taken the E6400 32M. It's probably the lowest hanging 70 pt of them all. 625x8 with any efficiency takes it, and that can be done with an average-ish chip.