7800 is the series. What's the actual model? 7850?
Either way the 7800 should perform better. Many cards require a lot of tweaking to get them to run at their best. What are your CGMiner settings? Are you even using CGMiner?
Yes I am, had 300khash and 150khash with the cards, but on the pool site it shows something different

Check to see if you're getting hardware errors. They're labeled as HW: in CGMiner. Are you getting a good number of accepted shares?
Also, how long have you been mining for? That number is sometimes an average over an amount of time like 24 hours.