Is AMD Phenom 1055T a good gaming processor?

you need to list your total system spec including graphic card, your PSU budget, and where you are in the world before anyone can recommend a PSU for you.

as for the the Phenom 1055T, the Phenom II x4 970 is the same price and performs much better in gaming. see the link below. I would pass on any current Phenom II x6 CPU.

http://www.anandtech.com/bench/Product/186?vs=147

My GPU will be either the AMD Radeon HD 6850 or 6870, havent decidet yet, my PSU budget is about 130 euros (180 dollars). I live in europe (Slovenia).
I think that the 6 core would be alot better in the long run.

If you dont OC the x6, the x4 is a better choice for gaming I think.

by the time you actually need a six core CPU, there will be much better ones out there. as for long run, ask the people who bought the original Phenom X4 how well their quads lasted them? They where getting blown away by Intel C2D CPUs like the E8xxx series in games. They became outdated months after launch. The current mid-level Intel quads like the i5 and even i5 dual cores out-pace the Phenom II x6 in games.

http://www.anandtech.com/bench/Product/145?vs=147

as for the PSU. I'm not familiar with Slovenia market. All I can say is buying a quality PSU is the best "long run" investment you can make in your PC. The top names in quality are seasonic, antec, xfx, silverstone, corsair, and enermax. a 500w unit from them is more then enough to power your PC with an ATI 6870, see the chart below. I also know they tend to be rather expensive in your neck of the woods. OCZ and Xigamtek offer solid budget units.

at load levels this PC barely breaks 300w with an ATI 6870.

CPU: Intel Core i7-920 @ 3.33GHz
Motherboard: Asus Rampage II Extreme
Chipset Drivers: Intel 9.1.1.1015 (Intel)
Hard Disk: OCZ Summit (120GB)
Memory: Patriot Viper DDR3-1333 3 x 2GB (7-7-7-20)