Vittoria Rubino Pro 3 are 28mm (mine measure slightly better than 27) have an iffy micro-knobby tread on the shoulders and is lightweight at 245g. Fatter at lower pressure might help, for example 75 psi front 90 rear. There's a Rubino Pro Tech version with sidewall reinforcement like the Gatorskins but the Pro 3 are fairly good as is. You could put the Tech on back and the regular version on front. Measure the clearance you have with callipers to see how fat you can go. Ribble sells them but the 28 are generally hard to find.
Photo showing micro-tread
http://store.fixie-factory.com/2659-...ro-3-black.jpg