Richard,
That sounds like a good combo too! F/4 would be notorious for perfect collimation, but imaging time would be significantly less than say f/7.5. Stephen, I was also going to say you can pick up cheap modded 400D here on IIS. That would be a really good way to start too without comitting to a cooled CCD (Not to mention filter wheels if you go Mono). I know Poita will be selling his QHY8 soon and for a great price, maybe email him and see what he says.
Anywhos heres the panorama I was talking about. Sorry for the poor quality, but it's a 105MP stitch of 3 images
As much as I hate Melbourne's weather, I do love the clear skies it gives up once in a while!