The four slots are split into two banks, so you'll have to install at least two modules. Go with the EDO modules and don’t worry about the size.

Which OS do you want to run?

The speed difference between FP and EDO is significant but small, the speed difference between thrashing and not thrashing is immense. If you can work within 64MB without thrashing, EDO is better, but if you use even one byte over 64MB, 128MB FP will be much, much faster.

For DOS less is better and 64MB is max usable anyway. For Win95, 64MB is overkill. Win98SE can use 64MB well, but anything that needs more will want a faster CPU. However if you want to run an NT-based OS (NT4, Win2k), you need all the RAM you can get and 128MB will be better.

Thanks everyone,
It will be mostly DOS and Win9x with a tiny bit of NT4 (Mostly cos I want to get Powerboat working on it, it did work at some point in development but would like to test it on retail). Maybe even OS/2 Warp as I used a bit back in the day (still have the floppy install disks somewhere!). I have another build lined up for 1999+ era games so 64MB EDO seems good.