yeah, most steel frames that i have seen have gone on the welds where the main tubes meet the headtube and bb! but i think it may be down to the quality of the weld more than the differences in size of tubing. i dont think it matter what size the piece is that your welding TO, its more the size of the WELD. on a different note, i'm prettey sure the larger diameter the tube is, the stronger it is. purely on the dimension side of things!