I have used APX100 and FP4 extensively. Both work well in either Rodinal, HC110 (dil B) or PyroCat-HD. Each developer has it's own look, so experiment to find out what it looks like for you. Then use the appropriate developer for the creative expression you want to produce. BTW I have used FP4 at both 64 and 125 asa's with PyroCat-HD. The 64 asa was with LF and the 125 asa in 35mm. Each produced excellent negs.

Developers are cheap, so go nuts!

Just our of curiosity, what is the Kodak equiv of Ifosol-S?