Fuel burn 43C VS 45-46C with same engines?

Hi guys I am the new kid on the block.
I am looking to buy a 43-46 C Sportfish for charter fishing out of Fl and NC in Jan 2015.
Fuel burn is a real concern of mine.
I want a good seagoing vessel that gets decent cruise speed and miles run for the amount of fuel burned.
I have been told that I can expect to probably burn in the 30-35 gph range at cruise speed of 20-22 kts, and 15-20 gph at trolling speeds of 6-10 kts.
Is this a pretty good assessment of the fuel burn, for a 45-46' sportfish and if so, what would the fuel burn be for a 42-43' sportfish.
Any help would be appreciated. Thanks!!

We have a 1990 Hatteras 45C. Just did a trip to the Forida Keys from Fort Lauderdale last week. We have 550HP DD 6V92's. At cruise 1950 RPM +/- 50 RPM we do 20 to 22 Average and we Burn Approx 35 to 40 GPH. While Trolling 600 to 800 rpm we get 1 to 1.5 Miles per Gallon. The boat moves pretty exact to 1 Knot per 100 RPM until you get above 1900 RPM then the hull breaks free a bit and gives you a touch more Speed.
600 RPM 6 Knts
800 RPM 8 Knts
1000 RPM 10 Knts
1500 RPM 15 Knts
1800 RPM 18 Knts
1950 RPM 20 to 21 Knts
2000 RPM 21 to 22 Knts
2100 RPM 22 to 23 Knts
2200 RPM 23 to 25 Knts
2300 RPM 25 to 26.5/27 Knts.

We ran from Ft Lauderdale to Islamorada. Spent the night. Ran at Cruise and Fished the Hump/Offshore Next day 12 to 18 miles out for 6 Hours. Ran back to Islamorada then Ran to Key West Next Day and Fueled. Total of 175 miles plus 30 miles of Running to fish and 5 to 6 hours Approx of Trolling. We burned 450 Gallons with essentially 205 miles at cruise and 5 to 6 Hours of Trolling. Hope this helps. Also of the boats you mentioned the 45C and the 46C are the better runnung boats. The 43C is an earlier version of the 45C with a shorter Cockpit. The 45 and the 46 are pretty equal in ride depending on who you speak with BUT, the 45C has the BIGGEST/Longest Cockpit in this size class of boat. It's 135 Square Feet where the 46C is 125 Sq Ft. Normally not a big deal but if your going to be Chartering it every little bit of space can help. If you were to find a Cummins QSM Powered Boat you would have a better MPG figure. They give the same burn per hour but with a few Knots more speed.

It's hard to break it all down on here but if you have any direct questions about the boats feel free to PM me, I'll get you my number and I can give you more details.

Captain Tony.

Captain Tony,
Thank you very much for all the helpful,info.I really appreciate it.
Thanks again.