Surfside Dan-I was talking about the 21V though....go sell a boat would ya!!
In reference to the fuel usage, anytime you add more weight you will obviously use more fuel. Especially if it's ass heavy it will be harder to plane off which will use more fuel.
I don't have any exact data as I refuse to look at the amount of fuel I go through (until tax time anyways) because it's pretty obscene.
I didn't upgrade all the way to the huge bags, but I upgraded the rear bags to 400 lbs each and will be adding some lead eventually. That being said, I have the 340 and the WB prop in my 21V and noticed zero difference in fuel economy from the stock ballast to my slightly upgraded.
If you have the 320 (pre '05) or the 325, you might want to look into a prop change if you're consistantly running alot of weight and can sacrafice top end speed.