Wow, lot's of great info and opinions! To answer one question, I have not given up on 531 or anything other than very low end/generic steel. That's basically my reasoning for the post. I am 170 lbs and only been seriously riding for about 3 years. I have a carbon bike and my tange 1 bike. I also previously had a Cannondale CAAD (super stiff aluminium). I notice a little flex on my Tange 1 bike compared to the carbon or caad bikes but not enough that it effects me. Initially I wanted to get a new frame that is a little more modern 130 spacing, 1 1/8 fork and so focusing on 853 or TSX etc. But, shopping for used and vintage/classic frames I feel like I've already passed up on some really frames in my price range recently such as a Merckx Corsa and an RB-1because they weren't a certain level of steel. But now I think I should open up my mind to things like 531 and other maybe "mid range" tube sets...especially because I want to stay under $500 and get a frameset that is in very nice condition