Just looking through the Egg and noticing the 6420 and the 6750 are just about the same price and the 6550 is about $30 cheaper. Judging from the specs, both the 6550 and the 6750 are a good bit faster than the 6420. Is this just a matter of an older processor not selling out fast enough or is their something I'm not seeing that would put the 6750 and 6420 on close footing?