Cripes, Dangermouse!
I'd definately run a 4 guage for that tbh. Yes, the Q-Dos one you have will do it, but I'd try and get the larger one or alternatively the Fusion kit is pretty good quality.
However, come mither me at work on Monday - I'm definately in this time - and I'll try and dig out the larger power cable we (did) have out the back... it's the power cables that make the difference to the power.
I'll look for it Monday morning and txt you if I can find it, if you'd like?