Pretty much depends on what you'd use the bike for. Your best bet is to ask the framebuilder themselves what they'd recommend. FWIW, I have a 631 frame I built on Dave Yates's course (his recommended tubeset for my "comfy non-racing road bike" spec) and certainly don't go around in tears that it's not stiffer or lighter. No doubt I might feel differently if I were doing crits on it or something.
Pretty much depends on what you'd use the bike for. Your best bet is to ask the framebuilder themselves what they'd recommend. FWIW, I have a 631 frame I built on Dave Yates's course (his recommended tubeset for my "comfy non-racing road bike" spec) and certainly don't go around in tears that it's not stiffer or lighter. No doubt I might feel differently if I were doing crits on it or something.