Hi sse william,
As Mr Robville says above you would have no problem with that set up. My own computer, which started off as a Gallant AMD-560 GTS250 bought from Dino PC Ltd for £399.00. has been uprated by me to the specs shown in my DxDiag below. As you can see, apart from the CPU, which is an AMD Phenom ll x2 560 Black Edition, is now very similar to the Specs you suggest above. I have no problems with SSE at all and can play with 25 fps on most missions with settings set to the highest levels. I changed the PSU from 500watts to 600watts, increased the RAM from 4GB to 8 GB, and changed the GPU from a GeForce GTS 250 (1GB)to an EVGA GeForce GTX 660 (2GB). In order to ensure things didn't get too hot I also fitted a case fan to help in cooling. I attach a picture of the inside of my machine and you can see the graphics card is quite a big thing wich needs plenty of space to fit it in. I should point out that the overall cost is still below your lower budgetted cost of £600.
Kind regards,
Angus.