Late 70's through Mid 80's Japanese top end frames for most builders are plenty good enough for your goals. Look for a Tange Champion #1 or Prestige tubing decal. Others will have suggestions on other tubing levels, but Tange is one of the usual steels for japanese frames of the era. I've had the opportunity to ride a Tange #1 Centurion Ironman, and even if it was two sizes too small it was a real joy to ride.