I am interested in a commuter/touring/rando type rig. I have my 72 Raleigh Super Course frameset, but I have also considered a new Nashbar Touring frame or a new Surly LHT frameset. Almost leaning towards the cheapo Nashbar because of my assumed (right or wrong) bb stiffness (alu vs steel). I'm relatively big and strong (gym and wattage) and although I understand commuting/touring is more about 120-180watts, occasionally I do like to put down some wattage (could make my brother's beautiful steel Guerciotti's inner chainring rub the chainstays). Any thoughts? If i get the Nashbar or Surly I am getting the Surly LHT fork...Once again most of my riding will be effortless 120-180 watts, but occasionally might need to represent...

Frame stiffness has little to do with frame material and a lot to do with frame design, although due to the increased chance of fatigue failure with AL, they tend to be built quite stiff. A stiffer frame also means a less comfortable ride, something that can be an issue on a longer ride. There are a couple of reasons for using a newer frame over an older frame, less issues with fitting newer components, which is something you may want for a long haul bike, you may be able to fit wider tires to a frame like the LHT. No reason why you couldn't build up the Super Course as a commuter with moustache bars and then get an LHT frame for your touring and rando.

Thanks.
Where would my new-to-framebuilding friend find the 'material' to add water cage mounts and downtube shifter mounts to the Raleigh?

https://www.cycle-frames.com/bicycle-frame-tubing/

Thanks

Really?

Yes, the frame designer selects the tubing dimensions, which are the biggest contributor to frame stiffness.....

Material can't be discounted, since the elasticity (springiness) parameters of steel, Ti, and aluminum(s) are pretty different. Both factors are key.

Meek, have you ever ridden an aluminum Cannondale? I'd see that as very stiff.

Is your friend going to build you a frame? Perhaps with such a ready source of expertise, you can learn about what to look for, in a frame that can handle a strong rider without chainstay rub. Clearly it's possible, otherwise the early decades of the TdF would not have happened!