Dude,you are on the way i am too!
i ordered 3 gigs of g.Skill at 1600mhz and i am waiting with my intel core 2 duo e4500 2ghz!
Probably,if your processor is too old(like mine)it will just not be able to use a 100% of the advantages a ddr3 has!
And also the mhz of your ram will fall down as well(i had ordered about half a year ago corsair value select 667mhz 2 x 2 gb ddr2 and at the cpuz at the memory it was using 333mhz from the available frequencies)
i don't know though if this is a correct answer