First of all, I'd like to point out that GTA5 is listed for a preliminary date as Fall '14
Second, I would recommend *not* going off a suggest build only, but ALSO only going for something which specs have *already been tested with LCPDFR*
Its no secret that GTA4 is a strange optimized game. I have an AMD dual crossfire setup that statistically should run GTA4 fine, but it runs barely playable(with CFX on and off, even though GTA4 does have a profile...). And with GTA4, the specific card matters more than picking Nvidia over AMD.
~ I know several guys with Nvidia setups technologically superior to my setup, and they actually have *worse* performance in GTA4.
Again, it doesn't matter the power of card, the manufacturer, or series. What matters is if its been tested and proven to work well with GTA4(as I assume LCPDFR is your main focus besides COD, which is an easy hand.)
And off your budget, you may want to look at pre-built. Custom built/assembled PC's only become cost efficient at higher prices. in a lower price-range, pre-built PC's are far more worth their money(specifically because of the bundled operating system, which you won't want win 8, and win xp ceases to be supported, meaning I'd suggest looking at Win 7 pre-built machine for the cheapest cost/hardware&OS).
I'm sorry, I have to cut you off there. First of all, because an Intel i7 2 core workbook processor will handle better than an AMD hex-core, and specifically better than an intel quad core i5 on low scale.
On top of that, GTA4 is only multi-threaded optimised for 4 cores(maybe 2, don't remember), but certainly not 6.
@ OP: a 2 core will suffice, esp if its a higher grade core. However, higher power cores introduce insane heat levels, which you do have to watch out for.
the suggested graphics card(GTX760 - 2GB), you may want to examine changing to a GPU with more VRAM. GTA4 does do a lot of rendering, however, there is also a significant texture amount(which I personally have trouble handling with a 2GB base VRAM).
@ davelaric, your suggested build, an H100i would not fit in. Most cases you could fit an H100i in, are only E-ATX & XLATX cases.
If you have any questions directly, feel free to PM me, I am not active on forums often.