Two of my clubmates have the Shock Wave, and I own a Wave Shark.

1) I would not call either boat fast, out of the box. But the 775 is definitely more powerful than the 550 and can be overvolted as well.

2) The Shockwave is probably around 10-12 mph. The Wave Shark about the same. Consider however, the Wave Shark is huge compared to the Shock Wave.

3) My Wave Shark is 5 years old and still going strong. I cannot say about the Shock Wave, but if treated well I don't see why it should not last a long time.

4) Yes, get the 775 by all means.

The Wave Shark is quite a good looking, scale model of a jet ski. Although, it is prop driven. It can be made to go quite fast too, with a motor and prop upgrade:

http://media.putfile.com/Wave-Shark-Megalodon