I'm buying a Streetfire frame sight unseen due to reviews and the fact that my shop doesn't sell a good aluminum race bike since we dropped Cervelo. I'm 5'10 and 150, looking to start racing. Medium or Large? I don't know sloping top tube sizing, but I usually ride a 54 very comfortably. 56 is almost always too tall in most brands. I found the M frame for cheap online... so I'm very tempted to go M. Common sense prevailed however before I hit the buy button, and here I am.