The model numbers have absolutely nothing directly to do with the clock speed. That the 4400+ has two cores running at 2200MHz is pure coincidence.
AMD model numbers are a guide for letting users know which CPUs perform best. However, they are not interchangable with any other numbers, including clock speed or model numbers of other processor families.
For example, the lineup of Athlon 64 X2 (dual core) processors ranges from 3800+ to 4800+. The higher the model number, the better the performance. However, they are not comparable to the classic Athlon 64 (single core) processors. The Athlon 64 3800+ is totally different from the Athlon 64 X2 3800+.
Likewise, Sempron model numbers are not comparable to Athlon 64s'. The Sempron 3000+ is much slower than the Athlon 64 3000+.
Finally, AMD model numbers aren't comparable to Intel clock speeds, either. The Pentium 4 3.0 GHz is not at all comparable to the Athlon 64 3000+.
If you want to see which processors are fastest, the best thing for you to do is to look at benchmarks. Anandtech, Xbitlabs, Tomshardware and other sites offer such testing.