Originally Posted by WizardOfBoz

I'm assuming that Loose Chain also holds an A&P* rating if he's TIG welding on airframes. I'd tend to give creed to what he says.

The strength of a frame with a repair weld will be less than that of a properly welded and heat-treated frame , unless you heat treat the repair welded frame afterwards. If you do HT the repaired frame you're going to have to repaint.

Lowering the seat of a bike significantly reduces your mechanical and physiological efficiency.

As others have pointed out, a longer seat post reinforces the seat tube to a point, but if your long seat post extends a long way, you still have a larger moment arm. Probably good to think about a larger frame if you can.

*Airframe and Powerplant mechanics rating, needed to work on commercial aircraft.