Instead of guessing at whether the kit bot is "strong" or "weak" maybe its time we actually did some tests and found out...
These are stress analysis tests my team did with inventor 10. All peices are the same length, and subject to the same variables, so it should give you a pretty acurate comparison.
Kit Bot Side Rail:
10-10 80/20:
Al Tube Stock:
These are all deformation tests. You may be suprised to find that the kit-bot rails are the strongest (which makes sense considering their profile).
I have only the vaguest understanding of how these tests are done. One of our mentors did them.
Despite these tests my team has decided to use 80/20 in our drivetrain b/c it will make chain tensioning easier (we had more problems with chains then frame breaks).