I have 27" in the front still, the tire although a year old and with a small boot on the sidewall, still rolls smooth as butter and the center tread seems to have a ton of life left. I also haven't bought a new front wheel yet. I've ran continental ultra sport 27x1 1/8 on the old wheels/components for over a year, and while they roll nice and smooth, there is no tread pattern (slick) so I have no idea how much tire is left, and they do not resist thorn or glass punctures very well at all, I had to run heavy thorn proof tubes in them which felt like it added almost 3lbs to the weight of the bike, lol.

I went with a 700c in the rear because that was the best deal I found available. I purchased a used mavic open pro / stainless DT swiss spoked / DA 7700 hub / DA 7700 9-spd cassette with a tire and tube for about $125 off ebay.

I don't know of any tires comparable to what I intend to run in 27" though, I have a michilin city 700x32 with a reflective sidewall that I will be swapping to soon.

I looked for awhile for anything with reflective sidewall, smooth rolling tread pattern, and highly thorn / puncture resistant (I live in goathead thornville, USA...socal)