what would happen if i dont. because when i used ddr2 with wolfdale platform, i had 2 sticks of 1GB 800Mhz and 2 sticks of 512MB 667Mhz. and they automaticaly set frequency to lower stick which is 667. well i overclocked to 800 later with no problem.
is it same principal for ddr3 as well or is there more complexity than ddr2?
Well, honestly, it'll be worth the extra $5 or whatever you save to have sticks that actually work. You have no choice; you must get that model, or else buy a new set of 8gb (but that certainly wouldn't save you money).