a 6 feet tall rider should be somewhere around a 58cm frame, however it is not an exact science. you can change your overall position/comfort is a few ways like trying a stem with a different angle or length. also you can adjust your seat on 3 different axis. your handlebars may just need a few degree rotation...
When you say you dont feel comfortable Im assuming this is when you are on your hoods right?? no-one feels comfortable in the drops.
My final thought, before everyone else tells you, is that you should make an appointment with a bicycle fitter at your LBS if you are unable to correct your position on your own.
2010 Kestrel RT900SL, 800k carbon, chorus/record, speedplay, zonda
1997 Trek ZX6000, 6061w/manitou spyder, xt/xtr, time atac