OK here we go! 6061: lightest, pretty solid, low density, but the elasticity index is lower than with the 7005 so it will break faster! 7005: heavier but still good, really solid, pretty good density, elasticity index real good because it is really high so it can take more damages without braeking... 7075: Heavy! Really! high density, and elasticity really low so it super-rigid! Coclusion: 6061 is for nervous and light frames, 7005 is for light and very long-life frames and 7075 is for heavy but really solid frames...