6950 beats 7750 any day of the weekhttp://www.anandtech.com/bench/Product/510?vs=535
the first number means "generation", sort of. 7 being the latest and 8 coming Q3 this year.
and the 2nd numbers show how "powerful" the card is.
x6xx cards ; pretty weak
x7xx cards ; budget/entry level
x8xx cards : performance
x9xx cards ; high end
and the last 2 numbers mean, higher they are, faster the card ( 50<70 )