Thanks Andy, as always you're right on the money.
I've gone back to the processing and had another run at it. I think I've managed to strike a better colour and contrast balance. I've attached a copy, but jpeg compression really doesn't do it justice.
I've uploaded it as a revision to my Astrobin as well.
I'm struggling with balancing the intensity of the Ha data with the OIII. I've found that a lot of the images online that really "Pop" severely down-play the Ha data to rely on the OIII to provide the punch. It's a difficult balance to get right.
I think i'm headed in the right direction, but it might still be a little magenta