I have decided to go for the capristo exhaust, see below for details from Capristo gmbh.
"Our sports exhaust system for the Audi R8 is freely programmable and back pressure-controlled. This means that there is a control unit for monitoring the back pressure. This control unit provides the possibility to individually programme the pack pressure one would like to drive. In this way one can reach the maxium performance. The portion of back pressure resulting in a loss in performance is filtered out by the
control unit.
Therefore this sports exhaust combines all advantages in both the lower and higher range of revolutions per minute (rpm), since the back pressure can be exactly dosed to enable the engine to gain
the maximum performance.
Most of the valve-controlled systems open the valves either dependent on speed or revolutions per minute (rpm). The engine, however, is neither influenced by speed nor by revolutions per minute but by back pressure, which is increasing at rising revolutions.
The control unit features an illuminated display showing all functions in plain text in 3 different languages (German, Englisch, Italian) and provides 3 basic modes to be operated via remote control, namely
a) Cruise mode - the exhaust gas valves open later
b) Sport mode - the exhaust gas valves open earlier
c) Open mode - the exhaust gas valves remain open
In both the cruise mode and sport mode one can individually programme the back pressure when the exhaust gas valves shall open.
The car is pleasant to drive without droning noise.
A big advantage is that the control unit recognizes the driver operation characteristics. If the driver aggressively accelerates, this is identified by our device by means of the kind in which the back pressure
is generated, and the exhaust gas valves open immediately. Usual accelerating results in a later opening of the exhaust gas valves.
The exhaust system is complety made of heat-resistant stainless steel 1.4828 (T309). This steel grade is comparable with INCONEL (F1 Exhaust material).
The price of 1 Capristo Audi R8 sports exhaust system amounts to Euro 3.500,-- + 19 % German VAT = Euro 4.165,00 ex works.
Freight charges have to be considered in addition to the price stated above."
I'll post with the result when I get it fitted next month - going to take a run to Germany to get it done.