Well, I have both the 5D and the 40D, and did evaluate the D300. For me, the 5D definitely wins on the basis of low noise / high ISO performance - the fact that the D300 has a higher ISO speed available is irrelevant as the signal to noise ratio is worse even than the 40D when both are used at ISO 1600. OTOH low noise / high ISO performance isn't everything (unless you're an astrophotographer).
Personally I prefer the old monolithic menu, the new one may be faster but is intensely irritating when you can't remember which menu you should be looking in. Otherwise the 40D has live view (don't care) and sensor cleaning (big plus if it works - it seems to for me, though some users appear to have found it ineffective).
They're all very capable cameras, and all are capable of delivering very good images when care is taken with post processing. The in-camera JPEGs from the 40D are noticeably inferior but the RAWs are very nice to work from, given a reasonable light level.
I like the way the 40D has extra custom settings - three instead of just one on the 5D - but hate the scene modes cluttering up the dial.
What I don't understand is the fact that 91% for an older camera seems to get higher on the plinth than 92% for a newer one ... shades of the Olympus "82%" controversy which has now degenerated, rightly IMHO, into a running joke ... neither do I understand why the 5D gets a lower score for image quality (37/40) than the D300 (38/40) when the text seems to indicate the advantage lies with the 5D. Unsurprisingly given the larger sensor.