If the G.Skill site shows its compatible with your motherboard you should be fine.
If the ASRock site says that a memory model is compatible, it is.
If it's not on one list or the other, then you are taking a risk.
I know on the x79 platform (with 8 memory slots) some kits only work at the advertised speed if you use 4 sticks, and have to be lowered for stability if you use 8 sticks. I'm not sure how that would play out on your platform.
Personally I think you should just go with the best one that is listed for your motherboard on either site. I wouldn't buy an unlisted one and risk having compatibility issues, unless you have a backup pair of memory sticks to use in case you need to return the new ones.