Is Quick Silver HP the same as Mercury HP ?

I woould say Yep, same company

Yes, same stuff with a different label.

Is that the stuff in a silver container I saw in Wall Mart ?

quick silvers is silver with a yellow label for high performance. I think the regular stuff is a blue or red label not sure.

I always get high performance althought Im not sure on the difference.

Yes . Silver bottle that says high performance gear lube
SAE 90
bottle reads
For use in all outboard lower units, jet pumps and Sport Jets 75hp and above and all Mercury MerCruiser stern drives.

My Mercury dealer told me that they are the same and that Quicksilver can be sold in other stores and the Mercury brand can only be sold at Mercury dealers.

About 4 dollars a quart cheaper also.

Correct.