Looking to get back into more road riding and train for and compete in a Centurion perhaps at the end of the summer. Lots of hills. Long hiatus after doing triathlons. Sold my Cervelo Tri bike years ago and I have a chance to pick up a Colnago C40 used, 51cm with a 51cm top tube. My experience has always been to get a really good bike used is better than spending the same on a lesser quality new bike and this would be in the top end of my budget. However, because I am not going to a store I don't have the luxury of a fitting or size choice. I will try the bike before I decide but wanted to get an idea of whether there was any point in trying it out. Getting mixed messages on what I could find online in Colnago sizing.

I am 5'4" and very proportional. Have about a 30" inseam. I ride a Surly Crosscheck 50cm comfortably. The top tube on the Surly is closer to 53cm from the current specs but also bought this a long time ago and don't know if specs have changed. Will measure tonight when I am home to be sure. What is the thinking? I won't bother trying it out if consensus is it will be too big and will wait for something else to catch my eye (or buy something less spectacular new).