I also have both, and agree that the 4" constant eye relief of the Conquest 3x-9x-40mm is great. However, to me at least, the optics of both scopes are excellent and kinda difficult for me to tell the difference. Yes, I think that the Conquest edges the Monarch, but not my much, and I have better than 20/20 vision.
Another benefit of the Conquest is that the reticles are etched, which I like. Still, I have NEVER had any problems with my Monarchs (or Pre-Monarch) scopes.
As far as prices are concerned, the optic zone sells the Conquest cheaper than any authorized dealer I know.
Note of caution, don't buy Conquests (or any other higher end scopes for that matter) from ebay. I have heard negative things about such purchases. A lot of people sell demo scopes and pass them as "Brand New." Sometimes you get a good deal, but with the amount of money that is involved, it really isn't worth the money. In fact, I'm goint to make a post about it.
Zachary