I'm jumping in late, but I think K-64 (or any slide film for that matter) can do fine for portraits. One thing I tried a while back with a roll of K-64was gelling my flash with a piece of 1/4 CTO (colour temperature orange) gel. It warmed up caucasian skin tone nicely, and didn't look gaudy. I'm pretty sure I got that tip from someone here. I did have to go to a film lighting speciality store to get the CTO (actually I had no idea one existed here), and I had to buy an 11x14 sheet of it and cut it up, but it didn't cost much.
Unfortunately my focus on the roll is embarrasingly bad, so I'm not posting any samples
I hear I can't get K-64 sent away for me locally anymore, so I may not be shooting it terribly much. Shame, really.