yes, Dual Channel RAM is faster than single channel ... some applications gain well,while other don't and perform same as single channel...
same brand in the sense...
ex. 2xCorsair DDR3 1333 9-9-9-24 , this is spec's
performs at dual channel with mentioned details.
non same brand
1xcorsair DDR3 1333 8-8-8-24
1xHynix DDR3 1066 9-9-9-24
if you try to run them in dual channel ,they both will run as DDR3 1066 9-9-9-24. Lower speed will run no matter how high spec you use other stick.. so here the high end stick is wasted or limited to lower speed stick.
ASROCK N68C-S is good for your processor. cost 2100
GIGABYTE MA74GMT-S2 is 740 chipset .cost 2650.
Tell me your main purpose for PC ,, if your purpose is for normal internet,movies, small gaming then above two are more than enough to use....