Sorry Ross wasnt able to assist, but if you described the problem as being loss of power, his suggestion wasnt too bad an idea, hook it up to a dyno and see what it is making.
So onwards and upwards. I took my car to Horsham developments yesterday and long story short, my secondary in line fuel pump for the supercharger was intermittent, I had no option but to leave the car there and get the train home, not easy from newbury to poole, first had to go further away from home to reading and then two more changes, 4 hours later back home for what should have been a 1.5 hour drive, so my day was 10 hrs in total, oh yeah and still got to get back there.
It was an absolute pain in the ass, but, small price to pay to get it sorted with someone who knows their onions, get it booked in with Horsham, suffer the inconvenience and enjoy your Zed again imho.