Why would you want to pay GTAIV on max anyway, it still looks like crap.
I love GTAIV to death, but not because of the iceenhancer mod, I don't care about the mods. I really enjoy the great gameplay and one of the greatest storylines I have ever played.
My overclocked and unlocked HD6950 with my 2500K at 4.5GHz handles it at full graphics, but the graphics card is running at almost full workload though. You are going to need some heavy hardware to run the game, as I benchmark just a hair over 60fps.
Not to mention you are going to need some serious power to run icenhancer as well. Personally, I play with the vanilla version of GTAIV.
If you want something that is going to be able to play GTAIV on the highest it goes with the mod, you are going to have to pay northwards of $1000 in upgrades. If you overclock the processor you have, I'm assuming an Athlon X4, you could probably play it on high with a decent graphics card.