This card shouldn't even be still sold. It's a dual-GPU chip based on really old technology. The HD3870, HD4870, HD5870, HD6870 are older models replaced by the HD7870. It's about 5 years old.
The best value is an HD6850 or HD6870 depending on your price.
FYI, GTA IV is very poorly coded and doesn't run well compared to similarly looking games.
You would likely be far better off building a computer based on a Z77 motherboard like this one:http://www.newegg.com/Product/Product.aspx?Item=N82E16813157306
It's compatible with the current 32nm Intel i7 and i5 CPU's as well as the newer 22nm like the i5-3570k.
There's not a huge difference in price between a micro-ATX motherboard system and a full ATX board but you do get additional expansion slots with normal ATX.