Upgrade help

Hey  

I mainly play FPS games such as Battlefield 3 and Far Cry 3, and I really like having a smooth, good looking experience. I don't want an AMD card, since I like NVIDIA and have their 3D Vision kit and a 120 Hz monitor.
Currently I have a GTX 560 Ti (Gainward something edition) in my machine, and I'm looking to upgrade it to the GTX 660 Ti (MSI Power Edition), but is this a good idea? Would I really see that much of an improvement? Some benchmarkers (Linus Sebastian from NCIX for example, VIDEO REVIEW) say that it has pretty much double the performance in games.
It's hard to give you my budget, since I live in Denmark and prices for components are higher then other places. If it's possible for you, you can try and search on this Danish website, EDBPRISER, in Dkk (the Danish currency) I have a maximum of 2400,-. This translates to just about 420 US$. I do have more money, but I'm also getting a new headset. The MSI Power Edition GTX 660 Ti costs 2.277 dkk, roughly 400 US$. Yeah, *** is pretty expensive in Denmark  .

If you could help me with this, it would be very much appreciated. I really just want to know if this is a good idea, or if I should aim for a different card.
Thanks in Advance
-Drugoli


System specifications:
MSI 770-C45
AMD Phenom II X4 965 BE (OC'ed to 3.7 GHz)
2*4 GB Corsair Vengeance DDR3, 1666 MHz CL7
Gainward GeForce GTX 560 Ti
128 GB OCZ Vertex 4 SSD (boot, actually upgrading to that either tomorrow or the day after that)
500 GB Green WD (data)