Painful as this is, I think that the best way of getting a better frame rate will be for me to ditch the warping of the flames which means that I'll be able to make this routine viable for a demo.
I'll be releasing the full source code for this effect once I've got the demo coded.
I guess that it's hard to take a step back and scrap code that has taken a lot of work, but I have to admit that it looks probably a fair bit better without the warping. Oh well

Thanks for the testing guys, you've saved me some embarrasment from releasing a slow routine.