I've been looking for a PC for a while, but it is just so hard to find good pre-built systems for gaming. I've found (what I think is) a good system, but I want to get opinions on it. My biggest concern is regarding the 1055T, because I really know very little about it.

Here are the specs:

AMD Phenom II X6 1055T
ATI RADEON HD5770 1024MB
4 GB RAM DDR3 1600MHz (2x 2GB)
ASUS M4A785TD-V EVO/U3S6
1000GB SATA-2 HDD 7200rpm
22x DualLayer DVD±RW DVD Writer Multi Format SATA
600W PSU

Its so good that its overkill, does that help?

For gaming, you'd do better with an X4 965, which is the same price IIRC.  Though, with Turbo CORE boosting it up from 2.8 GHz to up to 3.3 GHz, since games won't be using all six cores, the difference between the two wouldn't be too major either way.

So, I'd go for the 1055T if you need six cores, otherwise, 965 or 955 or something.

Short answear: no, get i5 750.

Long answear:  you can count number of games supporting more than 4 threads with the fingers of one hand and even those offer like 5-10% adventage

i5 750 is for dead socket while 1055T is for amd's newest socket so you can easily upgrade in the future.  Also when games start to support more than four cores 1055T will be more powerful than i5 750 so it will be more futureproof also in that sense. Difference nowadays is not that big anyway because 1055T has turbo core technology.

Almost every review of X6 series will clearly states i5/i7 is better value for gaming.

And please can we not joke about platform longevity ? If your plan is to get am3 to later upgrade to cpu than finally might be able to catch current lineup of intel cpus good luck.

Personally i would drop down to the AMD 955 or 965 and Then overclock it. ANd then spend the Xtra $ on a better graphics card. Something like a 5850. Barely any games take advantage of even Quad cores let alone Hexacores. I think the money would be better spent on a faster quad core and a better video card

Hexacore is a waste for gaming at moment. Getting a Phenom II 955/965 will be better now (and a lot cheaper as I just compared those two chips myself for my upgrade last weekend) and since AM3 is going to be used for quite awhile you can get an even faster hexavore or even an octacore down the road when games are actually using lots of cores.

Like everyone else is saying, you don't need 6 cores. Just a waste of processing power. It's better to overclock a quad core.

i7 is all over kill and i5 750 is like $250 compared to a 955 which is about $180-$200 so by saving the money and putting it into memory and graphics you are getting a better system.