Just tested King's Field. Performance is very good. It is more responsive than on native hardware even. However, there's some flickering and you can see white dots where some of the polygons touch.
Just tested it out with the PSX version of Diablo. Sound was of course garbled. The game felt a little slow to begin with at 750mhz but I believe the PSX port felt that way on original hardware too. Saving to the memory card resulted in the SDHC I/O light going solid green and the entire Pandora...
Hmmm. I tried loading both the PSX ISOs I had on hand, Diablo and King's Field, from my SDHC card and got "LOAD FAILED" in both instances. Also, does this emulator require a copy of the PSX BIOS? If so, where does it go?