Great capture. Did you use the higher ISO intentionally to isolate the background more (faster shutter)?
I'll be searching the forums for your shots with the 20Da, but do you maybe have a gallery up?
Yes I used the higher ISO for this reason. Believe it or not as astrophotographers we routinely use higher ISO's to capture more light then deal with the noise in post processing.
I'm putting together a gallery but it's not complete yet.
Here's a few links though.
This is the famous HorseHead (1.5 hours @ 1600 ISO)- there was high cloud though which interfered with the shot so I'll be doing another soon.
This one is the antares region in Scorpius and was a single 90 sec @ 1600 ISO using the 85mm L f/1.2