I've only managed to fist one woman, this was going back a few years and she had a complete bucket cunt (no complaints though, I love any type of pussy, large or small!) but she encouraged me to fist her, she loved the feeling of being completely full and she insisted on having a couple of my fingers up her ass at the same time!
My wife can take four fingers easily, but I struggle to get my hand in there, even though I pull my thumb under my other fingers I still can't get the knuckles inside her!
My fuck-buddy however, is a total ass-freak; she loves it when I put three fingers in her ass hole! She wants me to eventually stretch her that much that she can take a fist in her ass! Strangely though, she can only take three fingers maximum in her cunt, am I the only one that finds that a bit weird? But I'm not going to complain about it