for single dual and quad threaded games the 1st, 1 is actually slightly better. no it doesnt support dx11 but that card doesnt have the grunt needed to run it. the 550 is basically a rebadged gtx 260 with dx11 added it has no real advantage performance wise. the main difference is the cpu. and the quad core will give fairly similar or even marginally better performance than the 6 core in games due to the weaker single threaded performance that the cpu is crippled with...
for my money though i would buy neither. i would get an i3 or i5 over both.