Should I upgrade phenom ii x3 720 to x4 960T?

You will not see much of a difference since most games only utilize up to 3 cores. Difference in clock speed will give a little bump and the 960T would be a little future proving. Both CPU's should though overclock well and your X3 possibly unlock a core if you have not already tried.

For gaming maybe a little improvement the biggest improvement is in multitasking.

+1 rolli

OP: Are you overclocked? What GPU(s) do you use?

I'd spend a few bucks more for a 955. Higher base clock and lots of OC headroom.

EDIT: I'm operating under the assumption that your MB supports 125W TDP processor.

The easy answer is no, overclock the cpu as far as possible and as rolli mentioned try to unlock the last core. What motherboard do you have ?

I can't unlock the last core as the system would not boot, but I have my CPU overclocked to 3.4ghz right now. My motherboard is the Asus Sabertooth 990FX. I got this motherboard because I was originally planning on getting the 6 or 8 core bulldozer CPUS, but read a lot of comments about how phenom II is much better than them.

My GPU is the 5850 1gb. I plan on waiting for AMD 7000 or nvidia 600 series cards for a few months before upgrading this part.

When you tried to unlock the core was your system overclocked ?
Have you tried adding more voltage when using the base 2.8GHZ clock before unlocking the core ?

I'm a beginner overclocker, but when I tried to unlock it I had it on default clock speeds and I believe I did increase the voltage a little bit. It wouldn't boot up and I had to remove the battery on the motherboard to reset it back to default settings.

If it does not unlock then it makes the upgrade viable. The 960T is a 2 core disabled X6 and is a 95watt CPU with good overclocking potential.

I went from a 740be to the 960t and it is definitely noticeable. Much easier to overclock than the 740. about a 20% improvement on benchmarks. It runs cold and doesnt use a lot of voltage. I was able to unlock 5/6, normally just running 4 cores at 3.6g with no problems. With a small voltage increase, [to 1.35] and just raising the multiplier, it runs at 4.0g stable. Good chip. Try disabling single cores, my 6th wouldnt allow it to boot, but Core #4 [#'s 0-5] was good enabling 5 cores. Steal at the price.

I made the switch from an X3 to the X6 1100T recently, and I don't really see all that big of a change in gaming on Source engine, although to be fair, Source tends to be a single-thread, CPU limited engine. I have yet to test the core out for video rendering, but I think it'll be a lot, lot faster.