Well, well .... the SEM does indeed make a big difference! Switching back to stock mani and TB this morning felt horrible, felt like the engine was sucking through a straw - so I came straight back and refitted the SEM, just finished half an hour ago!
This time I took my time and cleaned off all the surfaces, rubbed down the phenolic spacer, cleaned everything with IPA, wrapped all the threaded hose connections with ptfe tape, made sure everything was tight and sealed. I sprayed the new gaskets with the blue Hylomar instant gasket spray before fitting, so hopefully they'll make a better seal this time. I also replaced all the vacuum hosing with new blue Forge silicone . I sealed round the IAT sensor with Hylomar too. We'll see now if the pressure drop fault code goes away now, if it doesn't then it's the 80mm TB that's causing it.
I also extended the injector wiring so there is no strain on them now, they're all properly soldered, heatshrunk and covered with black braided sleeving.
So all in a very busy day but I feel very happy now that the SEM is buttoned up properly, plus it is doing an awesome job so it is staying on the car, I'll just have to save for a wee while longer before going GT28RS - lol!!!