except missing the l3 cache is something major. its the reason why phenom II thrash the athlon II's, its generally around 10-20% better performance clock for clock/core for core. Unless you get your hands on the early x4 620's, its nowhere near the value for money as a x2 550. the early x4 620's were actually unlockable to full Phenom II x4's, these propus cores 620's at most overclock to 3.3-3.4, the pre-propus models could go up to around 3.8. while people are running x2 550's at 3.8, all cores unlocked using the stock cooler (load temp somewhere in the 60's). The furthest i've seen someone running a 550 is around 4.1
http://www.anandtech.com/bench/default.aspx?p=106&p2=97
http://www.bit-tech.net/hardware/cpus/2009...20-cpu-review/6
http://www.bit-tech.net/hardware/cpus/2009...20-cpu-review/7
yeah its quite close in some things, huge ass gap in other, but after unlocking/overclocking. the x2 550 is a much better cpu if you intend to game.