Hey guys, I know this probably comes up a lot but maybe not so much in this forum. The reason I ask is because I'm considering buying a vintage steel frame.

Currently my main ride is 2011 Bianchi steel (from the Gran Fondo line). It's a "59", which according to their website comes from the C-T measurement of the seat tube. When I measure it myself, it looks like 59 C-T (top of the seat lug) is just about right. C-C, though, it looks more like a 55. I'm about 6'1, and every time I measure my inseam I come up with a slightly different number (usually 89-91cm). But using the old x0.65 method, I always come up with at least a 57 C-C size.

On my current bike, I have about an inch and a half of clearance when standing over the bike. Since I'm considering buying an old frame, I'm wondering what I should make of this when choosing a frame. Since I'm likely to buy a frame online like on ebay or something, should I use my Bianchi's 55CM C-C measurement as what I want, or should I go with what my inseam size tells me I should do? My standover height appears to be about 35".

EDIT: It just dawned on me: could the slightly oversized tubing of my modern steel bike be the difference? It seems that measuring C-C on two bikes with the same standover height, the one with oversized tubing would yield a smaller measurement while the vintage tubing would yield a larger measurement - even if they seem the same size to the rider. My old Peugeot which I bought without knowing anything about road bikes is definitely too large for me, about 60CM C-C on both the top and seat tubes. I have about 1MM of clearance standing over the top tube, and the reach to the handlebars is truly ridiculous. But it seems like a few centimeters smaller (57CM) would fix this problem.