Sorry dude, I've done both ways (27 rear, 700 front, and the reverse). You'd have to be some sort of Jean Grey mutant in order to sense the difference.

My beater has a 27 front / 700c rear. Feels fine to me. In fact, it feels great!

I tried that too and could sense the difference at first..sorta like getting on someone elses bike. But its so slight that it doesn't really matter and the feeling of it being slightly different goes away after a few blocks, so its basically irrelevant. I've used different size tires on my mountain bike and the difference there is similar, but again, it doesn't result in significant handling differences.

I want to chime in on this thread, because, at some point I may convert from 27 to 700...

So...for clarification...

A 27" wheel is 630mm.
A 700c wheel is 622mm

8mm diameter difference. (5/16 of an inch)
4mm radial difference (or about a smidge over 1/8 of an inch)

So if I can drop my brake pads a smidge over 1/8 of an inch...I can make do this conversion easily.

Correct?

If you can drop your pads 4mm you are set.

Assuming your frame does not have ultra narrow clearances that is. Though pretty much any 27" frame will probably have whack loads of clearance.

I had no problem fitting 700x38 tires in a beat old nishiki designed around 27" wheels. I did, however, have to use a cheesy-ass BMX brake to reach the rims because the rusty universal centerpull just didn't have the reach.

yupp I at times have put 37s on my conversion