gains from alum. driveshaft?

Over a stock lt1 driveshaft?

no shakes at 80 lol

It helps some from a performance stand point but not enough that you will notice it driving around.

Lighter rotating mass...... Possibly quicker ET around .1~.3

There is a dyno test on WS6.com (link doesn't seem to be working today) that showed about 2-3HP savings with the aluminum DS. Hard to believe that could ever net 3/10'ths.

One thing to consider is that the aluminum shafts don't have quite as high of a Ultimate Torsion rating as the steels do.