Does the GW-8 software allow you to import MIDI files?
That would be the door to user style creation, I guess, and to be honest, I prefer to do all my editing in Cubase (because of the power and familiarity) before I assemble the style, anyway...
And, I'm still confused... as radically different as an M50 is to the GW-8, why is this the next choice? Surely, if that's what you would need, you wouldn't even LOOK at the GW-8 in the first place (or vice versa)? Loop and arp WS's have virtually NOTHING in common with any arranger, either sound, OS or style-wise...
It's still kind of like saying that, if the T3 doesn't work out for you, your next choice would be a FantomG

They are like chalk and cheese!