I am thinking the contention that aluminum frame is a much harsher ride than steel is kinda overblown. Years ago I went from a Motebecane Grand Record with a 531 frame to a Schwinn Aluminum frame and didnt notice the difference at all.
I am going to build a fixed gear bike as soon as i find the right frame used. If I can get a nice steel 531 frame for a decent deal I will scoop it up. If i cant find one soon, I will take a 88 through 01 Schwinn aluminum frame from a 564 or the other couple models from that time and build one. I love that quill seat post everyone else hates lol.