From looking all those sites previously, it looks like even within the same card with all the same specs, different manufacturer's cards perform a bit differently. For example the XFX and HIS cards seem to perform better than the others in most cases. The Sapphire and MSI cards all seem to be middle of the line, the ASUS, AMD and Gigabyte cards seem hit-or-miss. That's not actual analysis, just what it sort of 'seemed like", and it was different per card. Also the IceQ and Frozr cards and such performed much higher H/s than other versions of the same card...however they also sucked up a lot more Wattage in most cases.
From what I saw, from a good manufacturer, with good settings and optimal cooling, a 7850 seems to be able to hit high 300s or just barely break 400. Taking a ~370H/s 7850 at it's routinely reported Wattage of 130, that's a 2.84H/s/W which is very competitive with other cards. In fact, depending on which manufacturer and how your tuning goes, I'd say the 7950 or 7850 are your best cards for power efficiency, with a fair amount of certainty at this point. The 7850 is also almost undeniably your best card in terms of H/s/$.
My Asus 7850 will only do 305@1050MHz with I=14. The card won't go any faster without crashing the driver.
My Gigabyte 7950 stock (no overclocking) will do just over 500GH/s each, the pair give an average of 1.046GH/s according to cgminer. Far, far better cards, considering I got them both used off the Bay of E for the same price I paid for the 7850 new.
What are the settings other than intensity on your 7850, and how hot is it running?
The 7950 is definitely a good card and 500+ seems totally doable on it by all accounts, but getting 2 7950s for cheaper than 1 7850 is pure insanity. You got an awesome deal.