Hi there!
tRbz: It depends on the memory, if it is Dominator, it might work slightly, but if it is normal or the value ram, then it should be fine for sure.
marcus60: Thanks for confirming. The OCZ Reaper are known to be a problem with Mugen Series and lots of other coolers. Thamks for confirming though, I'll add the link to the list. Hope you enjoy your Mugen
SocialUser: Mugen CPU Cooler should be compatibile to the Gigabyte GA-MA790X-UD4. I could not make the real test, but looks like the usual layout that fits. The Cooler will be mounted horizontal when seeing it inside a pc tower case.So either the fan needs to be on the short sides or you have to use teh vertical airflow...