Get another 40HP and rig that OX with twins...now that would be something! I wish I had a spare 70-90hp laying around, I'd rig it for some fly fishing...I love that open deck.
Anyways, there is a 17 Del Quay Dory Center Console for sale on Hampton Roads craigslist...its listed as a trade for a camper but has a price tag of $4000 also. Think of Del Quay as the British version of Boston Whaler's Montauk. Tough boats.
Good luck with your search...it's a buyers market....wish I was in it!
You might try thinking about a pontoon as well. You can get them cheap and they make great duck hunting platforms. Easy to camo rig, lots of room for carrying decoys/dog/other person, light enough for your 40 and travels well in shallow water.
Whaler "Bass Boat" model...with front and rear casting decks. Very cool. More functional for fishing that my Whaler Montauk for sure. Not sure about duck hunting. You seem to have alot of options in your budget range. Given its a Whaler, I bet you could use it a few years and sell it for even money.
Whatever you end up with, please keep us informed...I love dreaming with other people's money!