Save the money and go for the 955. The max clocks for both will be near identical. An x2 can be unlocked on certain motherboards. It's a gamble though and will almost certainly hurt your max OC. You should really treat it more as a dual core chip and if you get lucky enough for 1 or 2 more cores it's just a bonus. If you need 4 cores then buy a 4 core processor and save yourself the heartbreak of a possible failed core unlock.