Since the original pictures, I've fitted an Arctic Cooling Twin Turbo Pro to my 5850, replaced the Xonar DX with a D1, fitted an Alpha Cool LCD where the two blank covers were (shows CPU usage, network usage, time etc whilst gaming).
No chance on getting a 5970 in there with the WC as well. Not only that, they are a tad pricy for me.
I'm not sure whether I like the side fan, but if you can't see it I guess it makes no odds.
I've started overclocking it a bit (to 3.5GHz on CPU, 2.4GHz on NB, not bothered yet on HT/SB, and have played with timings on the RAM):
After 15 goes at IBT, overall OC is stable (though still need to play with the HT link), with undervolted CPU (from 1.35 to 1.30V so far), and temps don't exceed 48°C.
The new GPU cooler works wonders... Under normal gaming load before (with stock cooler at stock clocks) it was reaching 86°C after an hour's gaming. I've just posted this after gaming for about 2 hours, and max GPU temp reported from Afterburner is 58°C, and it's a lot quieter to boot. I've set up two OC profiles with Afterburner, as the stock 2D clocks seem a little unstable (157/300), so it now sits at 400/750 in 2D mode, and then boosts up to 850/1100 for 3D.