Looks really good ! You did not track ?
But you can easily use ISO1600 !
I got this pic of the same area (but a little bit smaller FOV)
http://sky.velp.info/skypics3/large/...20-stacked.jpg
by stacking 7 frames of each 30 seconds (tracked), no flat, 2 darks with DSS with the 40d + 1.8/85 @ ISO1600. Stars till +12.5 !
You can do the same with your gear even @ 8 seconds (then no tracking required), it's easy !