I'm getting a custom frame built in Columbus XCR stainless steel tubing.
Firstly, I know my fit very well, so that's not a problem. The issue is how various geometry options that are all compatible with the same fit will affect handling and ride feel for a frame made with this particular material.
I'm looking for a relatively stiff and aggressive ride with a modern feel, not for an old-school steel feel. That said, I don't want the frame to feel completely dead for someone of my weight (63kg). I want something that feels alive when making hard efforts out of the saddle and encourages me to push harder. I can put out about 4w/kg at threshold and over 5w/kg over 5mins, but I'm no sprinter.
What I'm most unsure about is seat tube angle and chainstay length. I need a relatively small saddle setback from the BB, but I don't know whether it is best to achieve that with a steep seat tube angle and a setback post, or a slacker seat tube angle and an inline post.
e.g., I can achieve a perfect setup on my carbon frame that has a 74.5 degree seat tube angle and a Thomson setback post with 16mm of setback. I can also achieve it with a 73 or 73.5 degree seat tube angle and an inline seatpost.
Is there an advantage to the traditional setup whereby the seat tube angle brings you forward and then the seatpost setback puts you back again (seems rather unparsimonious), or for a custom frame is there any reason for not going with the seat tube angle that allows you to use an inline seat post?
I'm guessing that seat post setback potentially provides some shock absorption, but might not a slacker seat tube angle also do that?
As far as chain stay length goes, should I be trying to shorten this as much as possible for a responsive ride (given that my fit allows for a steep seat tube angle in any case), or should I allow a little bit of extra length for "comfort"? My tendency is to prioritise performance over comfort, although only up to a point.
Another thing I'm uncertain about is bottom bracket drop. Most of the carbon frames I have been riding recently have pretty high BBs (e.g. 67mm of drop). I've heard that cornering and handling can be better with a lower BB, although I've found the 67mm drop handles pretty well with a 73 degree head tube angle and 43mm of rake (about 58mm trail).
My frame builder will doubtless have his own opinions on all of these issues, but the more I know and understand myself, and the more diverse opinions I can get, the better IMO.