It has two more CUs that are clocked lower and bring theoretical shading performance in almost exact same number (+~50FLOPS). It has the same number of ROPs too.It's not only more FLOPS, it also has more CUs, more TMUs and more ROPs
So, effectively Orbis GPU is 7850 and Durango is 7770, like I said. Interestingly, thats exactly the same thing Sweetvar26 mentioned too. That guy got everything completely right.
This is also off topic and I think I'm baiting a ban hammer on me.