I don't have an exact weight but I tow mine with my 1/2 Ton Suburban 5.3L without much problem and I live in an area with a more hills than I think you have. I have an outboard though and this old spec sheet shows th OB @ 3750 and the I/O @ 4750:
http://www.wellcraft.com/owners/info...anIOOB_86A.jpg
I'm guesing I'm around 6000lbs. loaded up on the trailer. I get about 2 MPG at cruise and I have heard the same figure quoted by I/O guys.
I have used mine to tow kids on tubes and the extra space is great. On smaller boats its always what do you do with the tube(s) after everyone is done. I can put two blown up in the cabin! If you don't mind the fuel burn its great for tubing.