Scott here is the exact same region taken with the 5DH and 300mm lens and Halpha filter. It was 6x3min at an ISO of 1600 so the exposures are roughly comparable. I will let you decide what improvement you have with that system but I think even Mr Magoo could see it.
Download both images and flicker between the two.
400K
http://members.optusnet.com.au/~cheekyfish/velabert.jpg
That system would be stunning for narrowband imaging!
Bert