Graeme,
Did you receive any feedback on this? The symptoms you describe are so similar to an Astra I was called to last week, same engine code. Absolutely flat until it has driven half a mile, and then poor performance, misfire, judders until 2,000 rpm, and then behaves fine. No dtc's logged under any circumstances. Starts instantly. Relative compressions perfectly even on Pico. Leak-off on injectors minimal. Smoked intake and no visible leaks. Scoped amps on injectors and they appear fine to me. EGR clean and responding. On road test, rail pressure and boost respond well and smoothly on live data. This has covered 70k, so the comment about cam wear is something for me to look into. It was a bit frightening to see an engine with 5k on the clock and all that money spent with no result,
Peter