Im going to wait until I have enough money to go top of the range or one away from it. Just tried GTAIV eyefinity, (didnt have display port adapter before which is why I wanted to know earlier) as expected it couldn't handle it. Correction: my pc got absolutely raped. Even with the lowest detail settings it could barely render frames. I know you guys told me this was going to happen but I was still surprised how bad it was. Half Life 2 manages 20fps full detail, its a shame Rockstar couldn't make the PC version more efficient.
HL2 and GTA IV are light-years apart in system requirements. You can play HL2 with a 10 years old P4 system, while GTA 4 will struggle on many of today's mid to high range PC's. Not a good comparison at all.
But anyhow, if you have your heart set on playing GTA in e3-way Eyefinity, a LOT more horsepower is required, as you found out. The rest of your system is well spec'ed.