The difference between the different series of aluminiums is the alloying content and workability. That being said, the only aluminium that I can honestly say that I feel a difference from is the Scandium alloyed aluminium, and I think that is from the perspective of being able to use thinner walls.

But the geometry, along with the saddle, seat post, tyre, and bar tape is really the factor, and most people would not know the difference in frame materials until they have spent over 1K miles and every dimension and component was the same.

If you look at the picture of just the frame in the original T2 post, it appears the dropouts are horizontal.

http://www.slowtwitch.com/cgi-bin/gforum.cgi?post=46356;search_string=aegis;#46356

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"The more you sweat today, the less you bleed tomorrow"

Scandium tubes typically have a smaller outside diameter. Differences in tubing diameter are more likely to result in different stiffnesses than tube wall thicknesses.

Given 2 otherwise identical tubes of 6000 series and 7000 series aluminum, no one would be able to tell the difference in ride quality. The 7000 series tube might be very slightly lighter or very slightly stronger, and, depending on how well the heat treatment proess went, staighter.