Thanks for all the input, guys.
When Nick first suggested the m50 intake mod I was reluctant as most of the guys in the US running this had also done cams (important observation: whilst this mod is almost unheard of in SA, it is prolific in USA, with pretty much anyone who races an M50B30 doing the upgrade).
I am reluctant to do cams, for cost and reliability reasons. I have chatted with Shane on a couple of occasions (mentioned by Bernard above), and he has been down the cam route, and is now back on standard cams, for reliability reasons. Shane has a quick, reliable car. I take his advice seriously.
Second important point: Reliability is EVERYTHING in a race car. We want power in order to be fast, but not at the expense of reliability. The dyno numbers are a metric, but never an objective.
Bottom line is I am absolutely convinced that there is power to be had through proper tuning. I think we've made a blunder going down the Unichip / Dastek route - this is simply not a specialised enough tuning solution for this engine with these mods. My fault - I was the dick who thought this would do the trick. We live and learn ...
There is of course the possibility that we've made some other blunder(s) with all the other fiddling we've done - thermostat delete, M3 OFH and oil cooler, catch can - messing with water and oil flow, vacuum lines, etc, but I dont see anything obvious. Maybe Nick's hack job with a dremel doing the port matching went awry

.
What seems clear though is that there are many example of people making MUCH more power with exactly the same setup we have - the difference being specifically in the tuning.
Now, to make matters worse, our LS diff wont be ready for this weekend, so we have no power and long gears.
Its going to be tough trying not to get run over ...