Never had an Asrock motherboard before but I heard that they're pretty decent overall.
CPU, MB (any of them), RAM and Case are good,.. AFAIK, HD6850 is a hair better compared to the GTX550,.
Only concern is your HDD,.. you better pick up something in the Black/Blue version of WD Caviars,. Greens are low-power/performance drive best used for storage but not for booting.
If your budget allows,. pick a small SSD (25Gb - 64Gb) as boot and practically any HDD for "mass" storage.