According to the big book of Amiga Hardware the max is 256MB for the Phase5 version. The card has two slots. For a max limit of 64MB it means max 32mb per slot. I dunno if this is the slot limit. Someone more hardware savy than me has to answer that.
But from what I can recall when I had ppc for my a4000 I think 128MB was max (32 per slot x 4 slots). Which is according to bppc 2x32mb... But then again big book amiga hardware..
Coul be that we're wrong? Hope so.
edit: Big book of amiga hardware says max ram for cybppc is 128, which is good news in a way for you?