Hey all,
Just a follow up on this in case anyone runs into similar issues in the future.
I have had the car in at the mechanic and they found a couple of things, related and unrelated.
They found that there was a pin hole sized hole in the downpipe but confirmed to me that this would be causing no issues at all as the rear o2 sensor seems to have been overridden. Would this be the case seeing it is a catless downpipe with aftermarket tune?
The main issue that they believe to be causing the problems though, is the fuel pump.
When the tested it they found it to have low fuel flow particularly in the 33% range, I believe.
Their explanation was that I am effectively having to use more throttle input to get the same result.
Hence why it is rolling on boost sooner than usual, but in actual fact would be normal for the produced throttle input... if that makes any sense at all.
The car is booked in tomorrow to have the work done, new fuel pump and filter. So fingers crossed they are right!