What single core processor is dual-core 4200+ equivalent to?

I've read that the clock speed of Athlon dual core 3800+ (2.0 ghz) is equivalent to the clock speed of the athlon 3200 processor, so it is like running 2 x 3200 processors. So what single core athlon processor is the clock speed of the dual core 4200+ (2.2 ghz) equivalent to?

3500+ for 512k cache per core
3700+ for 1mb cache per core

3500+ is actually more mid-range nowadays. 2 of them will make your system fly.

dual core, you can't have 2 3500+s on one mobo.