Gpu upgrade

I was put in a similar situation but with a GTX 570. So instead of increasing the heat and power consumption with a SLI setup, I upgraded to a single Gigabyte GTX 670 WIndforce OC X3. I love this card because its quiet, OCed, reliable, and benchmarked faster than the Galaxy 680 model stock. For $299 this might look small but it has a very cool design over a custom PCB. I recommend the newer generation card because if you do 560SLI then you might have to buy a 800W PSU. I use a OCZ Modular 600w for my 2600k, and GTX 670 Windforce X3.

Best I found
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

GTX 670 FTW :
http://www.amazon.co.uk/EVGA-GTX-670-Graphics-Card/dp/B...

would be best performance/ best option for your budget at 1080p.
If your resolution is over 1080p you might want to get something like this:
http://www.amazon.co.uk/Gigabyte-7970-Radeon-Graphics-C...

Here is what you might want to read if you dont want Gigabyte but gigabte is way better than I expected

http://www.anandtech.com/show/6159/the-geforce-gtx-660-...

You are right but, that has a reference PCB and airflow design which means LOUD!! under load.

You are right... This card is the one you should get without a doubt. You will be very hard pressed to find a better card for that price.

http://www.amazon.co.uk/EVGA-NVIDIA-Signature-Edition-G...

I was actually looking at this card not 20 minutes ago.

Get it, you won't be disappointed.

Hmmm. Not too shaby, I would say not too much bettter due to fan design. I read about once the fan kick in they can get pretty loud but not as loud as the other one. For his/her price range I'd recommend this too but it all comes down to whoever posted this topic. That said maybe he/she doesn't care about the heat or sound level lets see what one he/she picks that best suits them.    

With anyhing we just posted you will like they all have power. Whats your PSU

Its one of the cheapest if not the cheapest one on amazon UK... and it is one of the best ones... the others ones are closer to 350.

Yea you will need a decent 500w PSU but if he was using a 560 Ti before it should not be an issue. The GTX 670 and GTX 560 Ti use the same amount of power.
GTX 670: http://www.geforce.com/hardware/desktop-gpus/geforce-gt...
GTX 560 Ti: http://www.geforce.com/hardware/desktop-gpus/geforce-gt...

My PSU is ocz z series 750W

Excellent PSU   Can handle a GTX 680 if you wanted it too. I love OCZ its sooo quiet and never goes bezerk with fan throttle

Definitely, has been my favourite PSU I've owned by a longshot!