Don’t Remember if it was inside OMEGU or elsewhere, but you can get it here for 64 bit machines:
http://www.ntcore.com/4gb_patch.php
I have installed also the LAA application (Large Adress Aware) linked to my SH4.exe
With both, i don’t have any memory issue!
(Dunno where you can get it, but i’m Sure somebody will tell you)