If you look at this:http://www.tomshardw...ew-31534-6.html
Your 7600 is 13 tiers down from the top. Add to the fact DDR2 graphics memory is slower than DDR3, while DDR3 graphics memory is also part of the Playstation, the XBox and the Nintendo Wii. A worthwhile upgrade is any card three levels or more above what you have now, therefore in your case that would be a top-end 7900 series Nvidia or the X1800 series.
The next problem comes; things have move on so you may not be able to buy those cards anymore. The budget card recommended by Tom's Hardware if you read the rest of the article is a 9600GT or the HD4670, which are well above what you have now. It has been stated somewhere (I can't find where at the moment) you get better performance from games from replacing the graphics card than you would replacing the processor.
For all of the AMD cpus you've listed, the only real difference between them is the clock speed (which is pretty much irrelevant these days anyway), the cache (which strangely is lower on the 7750 than it is on the other two) and the amount of power they use. All you'll do by changing the processor is adding a few hundred megahertz. Many years ago when things were painfully slow it was worth replacing a 100Mhz processor for a 200Mhz processor because the difference was noticeable. These days, going from a 2400Mhz processor to a 2700Mhz processor you won't notice the extra 300Mhz so IMO it's not worth even thinking about.
Edited by Neil Jones, 20 March 2009 - 05:12 PM.