I can tell you that a cat-back exhaust makes a difference in power if you already have a 3" downpipe fitted. Since you have the CTS Turbo DP, I'd seriously look into a catback to complete the exhaust setup.
To answer your actual question between a TOP and a DV+, assuming you already have a Rev D DV as stock, I would most definitely get the TOP. Throttle response is better and you can actually "feel" the difference in your daily driving.
I say if your OEM DV is bad or if you have the older version, upgrade it to a DV+
I can tell you that a cat-back exhaust makes a difference in power if you already have a 3" downpipe fitted. Since you have the CTS Turbo DP, I'd seriously look into a catback to complete the exhaust setup.
No, I know how to drive properly. What's your point, mate? Do you understand the concept that you can add modifications to a car that do not necessarily add more power, but instead improve other aspects of the car's performance such as road-holding and responsiveness - which in turn leads to more efficient use of the car's current power, leading to a faster, better driving car?
A suggestion for the TOP would be the Neuspeed TOP. You can get one for the IHI turbo you have currently and with a very minor, and reversible mod you can use it for a K04 setup as well. The boost leaks people have issues with on TOPs is from the green o-ring that attaches the TOP to the intercooler piping.
Take my advice and get a new o-ring from VW and just make sure you install it properly and with due care not to stretch the o-ring when reconnecting it to the intercooler. If you do that, it won't give you issues. I've been running mine for more than 2 years now without issue.
If your gonna do a top might as well do a charge pipe too.