Fast loading could be the issue yeah
Myself I just use one 2x Micro SD to memstick pro duo converter with 2 32GB Micro SD cards, Fast loading is not really needed to be honest with a fast card (both the Micro SD are Class (10) that is super fast for any Micro SD) asides from that cso files load rather fast anyway unless you have a slower card I guess then that just makes me wonder how the Fast Load mod works... possibly better cache management
Most the time you don't save alot of space with cso compression, some games do compress very small though I guess, I don't find space an issue, if anything I have too much junk on it that I don't play.
P.S. Cvania asides from the re-translate is based on the jap version so some items are placed as they are in the jap version plus the 2 extra familiars that can only be found by cheating in the US/EU version
I'm sure I tried this before but may give it a second go and try and make the PSP version into a PSX CD, not sure what stopped me last time so that may not be possible.