For that site, going the AMD route is your best bet being that the prices are so high for the processor and motherboard, and you have a limited budget. However, the Intel processor (i5-2400) used in the Ebay comp would perform just as well if not better than the processor I listed above (FX 4100).
The 6770 I listed is also chosen to help you stay in budget... Like I said, that site is pretty high priced compared to some of the lower prices we have here in the states. The 6770 nets the same performance as the GTX 550 Ti, however is more appealing in price (at least here in the states). If you wanted to take a step forward in getting something that'll pretty much double performance, you should look into a 6870 or GTX 560.