Actually, the best AMD Dual Core right now is the 5000 Black Edition. It's because the unlocked multipliers will actually be useful. And you will be able to achieve +6400 (About 3.2Ghz) speeds on that processor.
Sadly though, to be able to dictate the multiplier, you NEED a decent motherboard. Budget motherboard do not have the multiplier settings in the BIOS.
I'd also suggest you get an AM2+ motherboard for 100% Phenom compability, because most older AM2 motherboard manufacturers usually will NOT make a BIOS update for Phenom compability (They want you to buy their newer motherboards , duh.)
Kirby : I don't get it...... O_o
Back to Phenom :
Well, according to some benchmarks I saw, the Phenom actually has better performance per clock ratio compared to the AthlonX2, even on single core processing, the main problem though, is that the AthlonX2's are running on much higher clock speeds than the current Phenoms available. Not to mention Phenom's are slightly harder to overclock.
AMD Phenom vs. Athlon Core Shootout | Tom's Hardware
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Current PC specs :
AsRock 945GCM-S
Pentium Dual Core E5200 @ 2912Mhz (233x12.5)
Palit Radeon 4850 Sonic 512MB gDDR3
2x2048MB Kingston DDR2 800Mhz RAM