You are talking about benchmarks only. Sure, you can see the difference on benchmarks, but can you tell a difference while surfing or doing whatever it is that you are doing on a day to day basis? I highly doubt that, unless you are doing a lot of video converting and compressing of files. There really are no games out there that will max your cpu out if you only have a 24" or smaller monitor. Also, I would rather save my money and buy a better video card than spend the money on an expensive cpu.
A benchmark means exactly just that, a benchmark. How well your computer does compared to others. You'll never know if yours is actually keeping up with others or doing poorly unless you actually know what the benchmarks are. That's why benchmark tests are important, and as far as I can see on the internet, Passmark.com has more than enough submissions to convince me on which parts are the best buy out there. Their benchmark program allows me to see what kind of frame rates my current CPU/Video Card gets compared to others. Now because I like PC games, this is important because I like to play the latest games at full graphic settings.
Tom's Hardware actually made of note of what you prefer to do by using a $75 CPU paired with different graphics card including the best then, Radeon HD 5870. They tested if getting a better CPU actually makes a difference in real world gaming experiences with Crysis, World in Conflict, and other graphic demanding PC games. They tested an AMD Athlon II x3 440 vs an Intel Core i7 920 using the exact same graphics cards. The conclusion was simple, the AMD does just fine if you don't play PC games that pump out some hardcore 3D graphics but if you plan on playing max settings in World in Conflict or Crysis then yes a nice CPU will make a difference. Their article proves that Passmark.com's benchmark program is actually accurate in telling how your system will do (at least here in terms of gaming).
http://www.tomshardware.com/reviews/athlon-ii-x3-440-gaming-performance,2619.html