And yes - mainly after the speed for VMX - but thought the 6 was fast enough - you don't think so?
Depends what you want to do with it, but if you're coming from the 300D, I think you'll be happy with the 6D.
The 6D just isn't as quick as the 7D, 5D or 1D, but will certainly perform waaaaaay better than you're current camera.
btw when I say 'speed' I don't mean how many frames per second it can shoot, I'm talking about how fast it focuses and then processes the images.
My 1D will shoot at up to 14 frames per second, but even for motorsport, the highest I ever shoot at is 8 and even that's pretty rare.
If there's an opportunity, see if you can get your hands on one before laying down the cash.
And above all, shows us some pics when you get it!