Core 2 3.2ghz w/ L3 cache and (from what I understand) more potential for overclocking; vs Core 3 3.0 ghz. Also; based on the reviews it is very likely that both will fully unlock to quad core. The thing I'm not sure about is the L3 cache as well as other architectural differences between phenom II and athlon II.
Just wanted to point out to the OP that you dont say "Core 2" for dual cores. Core 2 was an intel architecture which they used for there past duals and quads. I can see how you would make that mistake but im just lettin you know.
How is it not fair? AMD Phenom II X2 555 Black Edition Callisto 3.2GHz @ $90 shipped vs AMD Athlon II X3 440 Rana 3.0GH @ $75 shipped.
Maybe a better question to have asked is "How much does L3 cache improve performance, all other things equal" or "Why is phenom II more expensive than athalon II".
555BE is $99 on the link you provided. The Athlon II X4 635 is $99 from newegg.
AMD and Intel has been making CPUs for a long time and the know exactly where to price their CPUs. The X4 635 would be the better challenger to the 555BE, as not to affect the cost of the rest of the build. When the cost of a CPU is less or more, then it affects the overall performance of the comparison.
Tom's doesn't compare different priced CPU on the Best CPU article, unless they specifically wanted to find out about a niche. Ala i7 920 vs. Athlon II X3 440 article.
$15 doesn't seem like alot, but it could mean the difference between a better CPU cooler than stock, 5750 or 5770, 890GX mobo instead of a 880G mobo.
As I said earlier, I compared my Athlon II 250 (2mb cache) vs. E7300 (3mb cache) vs. E8200 (6mb cache). The AII 250 was toe to toe with the E7300, winning and losing on various benchmarks. However it always lost to the E8200, with differences around 3% - 5%.
I gambled with the 550BE amd have all 4 cores unlocked @ 3.55GHz stable. Even if you don't unlock any cores you should be able to overclock higher than the athlon. There is a chance you may unlock an extra core on the athlon and L3 cache though its alot less likely. At stock the Athlon is as good or better though.
I personally have both these cpu's and while i use the x555 for gaming, the x4 does fine & is certainly still a great deal....if your main goal is games and web surfing while keeping a cool and overclockable pc, go with the Callisto; it's always fun and interesting to try and unlock cores, overclock, etc..black editions are always great for this reason.
The AMD x3 or x4 are a good deal if your penny pinching or just trying to somewhat future proff a pc for regular computing and use of cpu-critical apps like adobe....I sell custom PC's to friends and college students and typically use the Athlon 2 cores for the price & performance....still, i have an E8400 wolfdale, and it feels faster than my x4 620 Propus core [most dual cores are just built for gaming it seems]...
The Athlon II X3 overall is much better than the Phenom II X2 for most tasks, but since most games are still dual optimized, the Phenom II X2 pulls a head there. If you look here, you'll see that the Phenom II can easily win most game benchmarks, but not by a large margin, the Athlon II still hangs in there. Take a close look at Dragon Age, the only truely multithreaded game in their bench listings, the Athlon II X3 has a huge advantage over the Phenom II X2. The same will hold true for GTA IV, Bad Company 2, and a handful of other games already out. In the long run, the X3 will certainly be a much better chip than the X2. http://www.anandtech.com/bench/Product/119?vs=120