plan on building PC this xmas.. which memory speed should I get the 800 or 1066Mhz? i want a 4GB kit .. is there a noticeable difference in games with the 2? not concerned about brand at this point.. just wanna know if the speed difference is cost efficient, i see 4GB kits for $60 as opposed to $120 for 1066Mhz. gaming system (i.e. far cry 2, crysis etc, gta 4..)