Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.
I say no tbh, If you've got a £130 spare then sell your 4850 and add the money you get from that to the £130 that you was going to spend on the gtx275 and get a 5850 instead which would be a proper upgrade.
I upgraded to a gtx260 from a 8800 which is about the same as a 4850 and I really didn't notice much of a difference.
I upgraded to a gtx260 from a 8800 which is about the same as a 4850 and I really didn't notice much of a difference.

An 8800 isn't the same as a 4850, an 8800 would actually be slower.
4770 4830 I think. The 4850 was between the 9800gtx and the old spec gtx260 IIRC.
cos you could get a brand new 4890 card for a bit less than 130. Or like others said sell the old card and add the money to a shiny new 5850 u would be spending like an extra 40quid at most and get a lot more performance plus dx11.4850 was very very slightly slower than the 9800GTX+/GTS250 and a little faster than the 9800GTX - really theres nothing in it in most cases.
8800GT is a bit slower but depends a lot on the resolution and game.
Coming from 8800GT SLI to GTX260 SLI I saw quite a big difference at 1920x and higher res, you'd have to be playing at 1280x resolutions to not see much difference.
£130 is a good price for a GTX275 - but I wouldn't spend the money on one now personally unless I had no plans for going DX11. Aslong as your running atleast a 3gig dual core CPU and atleast 1680x resolution, 1920x better, you should see a decent gain.
Im being offered a 275GTX for 130 quid from a friend, is it a worth while upgrade from a 4850?? Im running a E6600 system at the moment and am not too sure about where to go in terms of upgrading, is the 275GTX worth it at this price?
I'm sure the 4850 was almost as fast a gtx260 in quite a few games. bioshock went to ATI, CoD 3,4 and some of the quake games around at that time IIRC. Its hard to say how a 4850 would perform with the lastest drivers but I remember it was the bang for buck king of its day.
Theres a few games where the old 192SP card on old drivers wasn't much faster or even very similiar performance to the 4850 at lower resolutions.
Turn the res upto 1920x tho and it was ~50% faster overall.
The 4850 is capable of punching above its weight in certain types of shader heavy situations.
50%. I doubt the gap was ever that big, not a chance.
ohh btw is your cpu overclocked?