here's my two cents. I live in Germany where there are often no speed limits on the Autobahn. I travel very frequently from Frankfurt to (south of) Munich, a tad short of 300miles .
With 150 hp I easily travel at 100 mph without being flat out. If I had 50 hp more, I'd still travel at the same speed. It's a van not a Maserati. And if I have bikes on the rear rack I drop to 85mph in order not to stress the bike rack, but not for luck of power.
With the 4M I have the upgraded 17" brakes. I have the same brakes as the 199/204 hp. The Cali needs not only to be launched, it has to be stopped too. If I could launch it harder I might end up having to stop it harder, say in city traffic. And outside the city, it would hardly make a difference what my 0-60mph is vs the 199/204. In reality, how often do you floor it at traffic lights ? Never!
The 199/204 would definitely give an advantage only for overtaking and if you live in a really steep hilly area or you have to tow heavy trailers.
For me personally, since there are also many discussions on the longevity and maintenance costs of dsg clutch etc, I'd rather put less stress on the transmission with a 150 engine vs 199/204. Same on brakes disks and pads. It won't go through corner any faster with 150 or 199/204.
And for you guys in the UK , the 7th speed of the dsg is just like an overdrive to save fuel. At 70 mph the revs are low and the torque also low. It is inevitable that it will drop a gear as soon as there is a hill. But you get the benefit of low fuel consumption at such low revs. If you were in Europe instead, with a bit more generous speed limits, at 120/130 km/h you'll be chugging along at higher revs right in the torque area, and you wouldn't need a gear drop on a hill. With 199/204 no gear drop regardless, but you end up with an extra 50ps that you'll hardly ever need unless you are towing or live in a steep hilly area.
Did I write long enough? I think so ... I'll press "Post reply" finally!