Hi Mark,
Recently, I was in your situation... well, I never owned a R1, but I do own a H9 (hark, the hissing sounds!)... I did a deep study of the 40D, D300, and the E3 and I've made a practical decision based on the following conclusions:
40D:
Clear improvements over the past 10D/20D/30D models, relatively cheap, nothing exotic but you're not on your own. It's probably the best choice for low light because of the brilliant EF-S 17-55 2.8 IS USM lens. And for far reach, there's the famous 70-200 2.8L IS USM or even the 100-400 IS USM.
D300:
Exotic and has a lot of featuers (51 point AF, AF in Liveview, etc.). For me, I wouldn't pay the price difference for the added (supposed?) benefits over the 40D. The image quality between the 40D and the D300 are very close in most instances to call a winner, unless maybe in some special situations. Often I've seen people complaining about a lack of a good quality (non-kit) wide zoom with VR for the Nikon cameras. A recent test has shown the D3 and the D300 being not suitable for deep sky astrophotography... if you ever do that.
E3:
This is probably the best step in the right direction of the DSLR future minus the small sensor. Sure, it's a different technology that can't be compared directly to the standard sensor sizes but it has a lot to prove too. If this camera had a bigger sensor, I'd have bought it. A lot of people are worried about its low light performance. The 4/3 people claim that the smaller sensor allows smaller lenses and smaller cameras. The 410 and 510 are both relatively small... but the E3? It's huge. This is one thing that made me realise that the 4/3 people are losing their grip. Plus, because of the 2x crop factor, traditionally, you have to spend a lot on very wide lenses for wide photography.
All of the above cameras probably have better IQ compared to the R1, with the right lenses ofcourse. But if you have faith in the T* zooms, why not go for a Sony DSLR? The A100 is a really sharp DSLR (probably more than the 40D and perhaps even the D300?) and the and the A700 is supposed to be an overall improvement (except on sharpness) to the A100. You could also go for Nikon and get Carl Zeiss lenses, but as you might already know, there aren't any zoom lenses for the Nikon ZF mount at the moment.
Also, if you're that big on IQ, you should probably start by looking at the lenses you plan on buying sooner or later.
Hope I didn't make your decision harder
GTW
PS: If you haven't guessed, I went for a 40D with the 17-55 on Friday
