So I've reverted and gone back to standard. I can now put my foot down with out fear of scaring small woodland creatures. On a more practical level, the motorway noise is greatly reduced when putting your foot down and so all is right with the world.
The noise definitely turns heads, but I've realised now I want to stay a bit more stealthy.
On the plus side, if anyone is in the market for a 2 week old Progressive Parts Delete pipe for a 300 for a reduced price, drop me a message. I'm in the Reading, Berkshire area.