Do yourself a favor, take your pubic bone measurement, and go on that. You sound about the same height as me, and I have a 91cm and run around 80.5 seat height. I went with a 62cm Surly Frame, and I'm guessing the Soma will be about the same. Surly measures center to the top of the top tube. I built a Long Haul Trucker, 46cm (18.1") chainstays makes for a great commuter with panniers. It'll use V-Brakes, and the Sage Green looks way better in person. It will also fit up to 45mm tires. http://www.wolfenet.org/gallery/surly?page=4 for my build, http://www.surlybikes.com/longhaul.html for specs. Great ride, and yes I looked at the Soma's too. Go with at least a 60 for youself. Check out rivendell's bikefit page for more info on fit.