Best price to performance ratio among different AMD 64 Athlon X2?

Black Edition 5400+ @ 2.8GHz\65W for under $100.

^agree
and you can easy clock it to 3.2 with proper cooler. (My 4800+ @2.5 is running @ 3.2Ghz whole year already).

My X2 5400+ went a tick more than 3GHz on stock volts. I got 3.2GHz with 1.375v (228 fsb). Temps were not an issue. The only 'issue' I really had was with the '7' memory divisor of the 5400+ ((3200MHz divided by 7 = 380 x 2 = 760MHz ram speed using the 333MHz ratio))

If you want 'headroom' to squeeze every bit of performance for 800MHz RAM speed at 3.2GHz choose an X2 5600+ with an '8' memory divisor.

So the 5600+ would be better than the 6000+ ? But the 5600+ has 1MB L2 Cache while the 6000+ has 2MB

The 5400+ is now the X2 BE chip. That's actually better in that at stock you get DDR2-800 and I'm sure this is a new rev which should get a couple hundred more MHz. But it is STILL a 65W chip. If I had an AM2 mobo, I'd grab one.

The Athlon X2 Black Edition processors do not come with a [stock] heatsink/fan. While they are excellent chips, they probably aren't the best "price/performance" Athlon X2s.

On newegg, you can get a retail 5000+ that comes with a heatsink for $66. The 5400+ BE costs $90, without a heatsink. The 6000+ costs $112, which means it would basically cost about the same as a 5400 BE + 3rd party heatsink. And as far as gaming performance goes, the 6000+ is a tad better (with its extra L2 cache) than even a higher clocked Brisbane. The downside is that it runs hotter and uses more power.