As I said Mike I know what I'm aiming for ..................- my car is no garage queen and I spend around two or more hours a day driving so don't want to be deafened or have my fillings rattled out - I'm more interested in performance and I don't want to know its even there until I hit 3k rpm
if thats your case i'd say go for the invidia, i know you don't want the G200, which i run, but i found the clips on youtube are nothing like what i have, not only that, what you hear at the back isn't always what you hear in the cabin. plus alot of the you tube clips also have de cats fitted (often called test pipes).
i find the G200 great i don't hear much under 3k, it sounds almost stock, but over 3k its great, gives me the extra noise i wanted in tunnels, it doesn't drone on long drives and is a great all round exhaust. you also have the advantage that if its not loud enough you could add sports cats, or race manifolds at a later date.
i'd say get a drive out in the cars with peopel who have them, but i don't know anyone in the UK with a GT300 or Q300.