Bolo: when you tried the 700c, was it just as simple as popping a 700 into the fork? Did you actually try to move the brake pads down, or did you just eyeball it?
I'm thinking of converting the singlespeed to a fixed, and there are far more 700c track wheels available. (In fact, I think Harris Cyclery is the only shop to offer a 27" fixed wheel.) I won't need a rear brake anymore, so that won't be a problem. But how off would it be to run a 700c rear and a 27" front?