[Jnadke]

I guess it mostly comes down to your design/strategy. The geometry of Bosch and 8020 has certain strength benefits over standard structural extruded aluminum. However, if you don't plan on doing a whole lot of crashing and banging, and have the facilities and the manpower (experience), I'd use welded aluminum structural extrusion (either angle, channel, or possibly even square).

Steel is far too heavy and difficult to cut. I don't believe it's worth the weight versus the benefits for use in structural members. Bosch/8020 does have a certain ease-of-use factor to benefit, but if you support your frame correctly, you shouldn't need to ever take your frame apart to fix a broken/bent extrusion. Use cross-beams to support other extrusions and disperse impact energy accross your entire frame and you should be fine.