Okay it looks like my motherboard is only recognizing 20-22GB, even with 32GB installed. And after trying it again today I'm having the same problem I recall having before -- WoW won't read some of the files. Previously I thought this was from not being able to fit everything on the ram disk, but I tried it with all of WoW on the ram disk instead of just the data folder, and no joy.

I think this is because of a bug in ImDisk (the ram disk I'm trying). Running chkdsk on the ram disk shows it has lots of errors.

I'll have to try with a commercial ram disk.