The G56 Stage 1 kit is a nuts and bolts job that you can do yourself fairly easily. I think that G56 do a Euro 4 optimised system now, maybe? As the exhaust and filter are easier and quicker to do than the Centa mods, I would put that first and get the benefits now.
And the G56 extra power may quicken the justification/need for the Centa mod too
