Well it looks like people didn't get AMD's Memo from 2 years ago when they changed up the Model Numbers....hence this list for your understanding and I hope it helps people in deciding what card to get.
Old System
1) Ultra High End HD 5970 (Dual GPU's)
2) High End: HD 5870/5850
3) Mid Range HD 5770/5750
4) low End: everything else....
New System
1) Ultra-High End: HD 6990, HD 7990 (Dual GPU's)
1)High End: HD 6970/6950, HD7970/7950
2)Mid Range: HD 6870( 1/2 of a HD 5870)/6850( 1/2 of a HD 5850), HD 7870/7850
3) Low End: everything Else
I guess this is why you think your 7850 is so slow...Because it is. My HD5870 is still more powerful that an nVidia 550ti and it's how many years old? The only thing is I can't use PhysX with out a Patch and an nVidia card installed next to my ATI/AMD card.
Here's a link to a Video Card Comparison of the ATI HD5870 vs the nVidia 570 and pretty much beats it, not bad for a card that came out in 2008!
http://www.hwcompare.com/9048/geforce-gtx-570-vs-radeon-hd-5870/