This is just an opinion if I was going to use a bicycle for serious riding I would opt for a British or American KOF frame built on traditional lines. Ideally if it was a Brit machine one of Martin Copelands Bates or any other from the very few reputable frame builders left in the UK. Think it would have to be a modern Bates lets face it the first generation ride like a modern machine and the new un's are wonderful. If your American it looks like you are spoilt for choice, probably the deciding factor in this is length of delivery wait for your frame. I would kit this out with 70's or 80's gear. Simplex, TA, Huret, Shimano or Suntour, would have to use modern brakes though. Finally all you really need is three bikes a hack, your serious special and a classic from whatever era takes your fancy. Must have 32H x 40H rims still a tradionalist at heart when it comes to wheels.
Thats all for now. Keep those wheels spinning, in your memories if not still on the road. Be lucky Mick Butler Huntingdon UK.