From watching your videos, Danny Mac smoother than you are, and he's riding an inspired, and you ride mod frames. The Inspired is designed to 360 of stairs, it weighs like 2.2kg and is a much stronger shape than most mod frames. The main difference between all the aluminium alloys is cost, 6061 is weaker than 7005, but is lighter. (But when you compare the weight saving to drop in stregnth, it's not worth it really.) 7075 is very hard to weld, or impossible, I can never remember... Either way theres a reason it's never used in frames. You didn't mention U6? Not exactly sure of the stats but I think form memory that it's the best compromise of 6061 and 7005? If you make a super strong aluminium frame, it will almost definately be lighter than a steel frame of the same stregnth, and it will be stiffer. Otherwise they'd just make downhill bikes out of steel, they have very thick tubes and loads of gussets, but they still build them out of aluminium.