Subject is AMD 64 GHz VS AMD 64 GHz CPU. Not Intel CPU GHz vs AMD CPU GHz

When looking at different CPU reviews, it realy does seem that the difference between the different AMD64 CPU's are minimal even if the price difference is huge.
(Well huge prize difference for me with limited ammount of money ("married with children" u c))
You realy think the 4000+ is the best bang for buks? How come ?
Consider :
- AMD 64 3000+ ~115$ (1,8 GHz 512MB L2)
- 2GB memory ~140$
- GF 7900GT ~330$
-------------------------------> ~585$
- AMD 64 3500+ ~180$ (2,2 GHz 512MB L2)
- 1GB memory ~70$
- GF 7900GT ~330$
-------------------------------> ~580$
vs
- AMD 64 4000+ ~335$ (2,4 GHz 1024MB L2)
- 1 GB memory ~70$
- GF 7600GT ~180$
-------------------------------> ~585$
http://www23.tomshardware.com/cpu.html?modelx=33&model1=244&chart=68&model2=260AMD 64 4000+ 2,4 GHz is 25% more GHz compared with 3000+ 1,8GHz
Farcy bench mark 193.2 vs 163.8 ~15% faster
Quake III Team Arena 253.1 vs 208.8 17% faster
Wolfenstein 189,9 vs 159,9 ~15% faster
Too bad toms hardware dont test AH2
But you see what I am wondering abot ?
Then the thing about Vista. I was not planning to buy a new computer this year, and then again a new coputer when the first DX10 game i want comes out. Again, my money recurces are very limited....