I recently bought a used bike without knowing too much, though I certainly did do some research beforehand. I'm 6'1" with a 32" inseam, and my bike measurements are as follows:
Seat tube 57.5cm/22.5" ctc, 59cm/23.5" ctt
Top tube 56cm/22" ctc
Head tube 16.5cm/6.5"
The bike does seem a bit large compared to other bikes I've seen. When I stand over it there is about a 2" gap between the top tube and me, plus the seat is only raised about 4" and I can just about get my tiptoes on the group when I sit on it. The bike isn't uncomfortable to ride, though I do experience some awkwardness when I have to mount and dismount in traffic.
By the way, I understand that frame size is mostly a matter of preference, but as a beginner I have no preference, and the way I feel now, I think I'd be more comfortable with it slightly smaller.
Please just humor my ignorance as I am a beginner, but I am learning everyday.