I7 2600. How much of an upgrade?

At the same speed a 2nd generation Intel® Core™ processor would be around 30% faster at than an Intel Core 2 Duo. Due to the fact that you will be running a quad core over a dual core you will also get better performance based on how well the software is taking advantage of the additional threads. So easy answer is 30%+ almost all of the time.

Now since you are going to be using this for gaming I would advise that you look at an Intel Core i5 over the Intel Core i7 due to the fact that very few games can take advantage of more than 4 threads. This makes the hyper-threading on the Intel Core i7 have minimal value on a gaming system. Also you will want to top off at 8GB of RAM as you will not use more than that on a gaming system.

So here is what I would get: the Intel Core i5-3570, an ASRock Z77 Extreme4, 8GB of DDR 3 1600 (2 x 4GB) at 1.5v, and for the video card I would look at an HD7770 as it gives better performance at around the same price as the 650 or 550ti.

an i5-3570 will do just fine for gaming. The i7 is an overkill and most games won't utilize the hyperthreading support. 16GB of RAM in an overkill too. You can do anything you want with 8GB. No need for the aftermarket cooler if your not overlocking, stock cooler will be fine. Get an H77 or B75 chipset board, they are better. With the money saved from all of that, throw it into a better GPU than the 550.

http://www.superbiiz.com/detail.php?name=MSI-7870HK&c=CJ

or

http://www.superbiiz.com/detail.php?name=MSI-66TI2C&c=CJ

Even today there is not much of a difference between dual core and quad core when you relate it to gaming. The only difference you're getting is a few frames. But If I had to choose, I'd just go for an I5 3570. It's the best CPU to buy.

the i5 3570k is a better deal than the 2600 and is unlocked so can be overclocked, and cheaper, better bang for bucks and yea ur def gonna see 50% increase in performance atleast, that cpus ancient compared to the latest sandy stuff.

Thanks for all the replies. I got the 2600 because it was my plan initially. All I wanted to know was the performance jump from my core2duo to a 260 but thanks anyway for all the recommendations. I'm playing BF3 and Witcher 2 and noticed an increase in performance. Cpu usage is usually around 60-70% in BF3 and about 40-50% in Witcher 2. Is this normal?

Best answer selected by Jazzy1.