Is it a good upgrade?

I currently have a 3600+ (1.8 Ghz) AM2 Dual Core CPU. My friend wants to sell his 5400+ (2.8 Ghz) AM2 Dual Core CPU. Is there a chart that lists the performance differences between these two chips and is it worth going for it? He's letting it go quite cheap, but if it's not that big a performance increase, then I'm not going to bother with it.

I have 4gb DDR2 800 and a Geforce 8800 GT Graphics card.

Tom's Hardware - Benchmark SiSoftware Sandra XI

This has a load of things on it, but you can see a 50% fps improvement in supcom quake and UT

Yeah, you are basically getting near 50% improvement simply by the faster clock rate of the new processor. You will see a nice improvement across the board in most everything you do. Well worth the upgrade especially if he is letting you have it on the cheap.