Bit of an update!
A lot drier in Germany over the past week, so got the car on to the autobahns to have a bit of a play. First thing that was noticeable (to do with the new hfcs and y rather than the tune) was the amount of noise in the cabin has certainly increased! I also now have a bit of an exhaust rattle at around 2k revs which I really need to sort the next time I get the chance.
Anyway...
I am happy to report that the removal of the speed restrictor works (161mph max according to my satnav, wasn't looking at the speedo for obvious reasons!) and the bump in torque is definitely noticeable in the mid-range at higher speed. In real terms (and not just when driving at stupid speeds) this means there's when you have to slow down for a car pulling out into the fast lane, there really is no need to change down when you subsequently need to 'press on'. Just put your foot down and you're away.
The 161 is not top speed btw, there were still revs left...