the second one is better. but i suggest you go for the hd7770 rather than hd7750 if you can.
and yes the 1600mhz ram should make a little difference over the 1333mhz.
i personally havent used asrock mobos but after going through a lot of user experience they seem to be pretty good.
but why are u going with B75 rather than H61 or H67 or H77 ?