I am 6' 1" as well. When I recently purchased my Specialized Allez from an LBS, I tried out a 61 cm and a 58 cm. I have average proportions, and found the 61 cm bike to be slightly too big. The 58 cm bike fit perfectly and came home with me. If I was the one considering the Cervelo, I'd compare the overall dimensions of the bike to what Specialized shows on their site for a 58 cm bike. This should get you a size to start with. Unfortunately, 6' 1" is a borderline height for many bike makers. This means the 58 may fit great on one bike, but may be a bit small on the next bike.