A cheap job that's made me feel better.
I just spent an hour or so with the Dremel removing the step in the throttle housing. I also tapered the outlet of the housing so it matches the Irmscher inlet manifold better.
I didn't have the Chocolate Orange thing in my throttle housing.
I have looked at the spindle screws and they're massive. I reckon I could removed half of the spindle and use lower profile M4 screws. Must help air flow that.
Also because the linkage bush has worn I don't seem to be getting 100% open throttle.
Lots of little things that could help.