Gcard upgrade turned out to be a downgrade?

This is my old card

http://www.meshtechnology.co.uk/product-display.aspx?productID=1745

This was suppose to be an upgrade

http://www.amazon.co.uk/gp/product/B0094M2OFY/ref=oh_details_o00_s00_i00

I ran a couple of games with the same settings and looked at the FPS,generally the HD4850 is performing better.I've put in for sending it back otherwise I'm stuck with an inferior card.If anyone has any advice on cards let me know.

By the way I ran a driver sweeper to ensure the old driver was properly cleaned out.

This is the 2nd time I've bought a card further up in a series only for it to not give any performance increase(I think it was around the HD38xx series).

Well no kidding you wont see much gains between the 4850 and the 7750. You didn't do your homework to figure out what the difference was. You just thought that a new card would be better, and I am guessing your motherboard doesn't have PCI 3.0 just 2.0. So that would make the new card clearly worse.

As for the way AMD cards work look at the numbers the first digit is the series or card generation. So as expected the new card is a 7th gen while your older one is 4th gen. The next two numbers is the power of the card in the series. So think of it as 1 - 99 scale to other cards in that series. While upgrading from 5850 to 6850 the newer card is almost going to be slightly better but only a little.

While I am not 100% familiar with AMD cards being a NVidia person myself so I can't tell you the big gains and losses between these numbers I can say it is expected to be slightly better with the new card but I am almost 100% sure you need to upgrade your motherboard to 3.0 PCI to see it. Also take a hard look at your cpu because I bet its lacking in power to compete with your cards so its bottle necking the system.

If you post your PC specs I could tell you more.