It seems its set in stone in your head its the ecu...the reality of it is, it isnt!
IF you had a megasquirt jobby and were having these problems, then yes, I would suggest an ecu upgrade, but the hardware you have now is more than up to the job.
The on-paper-spec isnt like with a pc or laptop, where if its faster on paper, it usually is....you arent going to notice any difference in driving smoothness from a tiny bit more resolution on the map base, or sample rate of the processor! What you have is fine, its the calibration which is at fault!
Mapping is quite easy..its easy to see if u increase a number in this box, you see this much more on the lambda gauge etc....the art of it, which reflect massively the end result in terms of output and usability/smoothness etc, is understanding EXACTLY what, why and how you are changing the attributes of combustion, and therefore of the engine. This is what makes the difference.
I take it you are the same Mark who emailed me a few months back about mapping?
In any case, I can offer the details of the only other person whom touches my engines/cars..I cant emphasise enough how s**t hot he is at mapping! He's based in Carlisle,.and guaranteed he will have it running as it should. It might be a couple of hours drive from wherever you are based, but its well worth it. I drive 330miles to him for mapping, and will contnue to do so until I have my dyno.
IMO you are better off taking it to someone who actually knows whats what, than spend twice as much to buy a whole new set-up, and a few hundred more with someone who will do a half-cocked job....again.