I recently went up to a 3" cat back system and it made the burble a lot deeper. I have ran into a slight problem though. The flange on the old downpipe has been bent into a concave shape so the new centre section doesn't sit flush. Luckily for me I have the decat downpipe ready to go on so it's only temporary. I've had to use a bit of gun gum to seal the joint for now.
About the back pressure Ven, in my numerous chats with Duncan @racedynamix he has explained to me that the turbocharged engine doesn't like back pressure hence removing cats and silencers gives quite a considerable power gain. Also from my experience with n/a cars they need the back pressure to produce a decent torque figure.
I have a video on here showing the zorst burble with the 3" cat back system and its very distinct but not very loud at all. I'd recommend going up to a 3" as I went from 211hp to 234hp just from the centre and rear exhaust.