Good luck with the new ride!
I don't have an answer to your question, but you should be able to figure it out once you dunk her. I'll assume this is a 4 stroke engine?
For reference, my boat is 21' and loaded weighs around 4000lbs. At 3500rpms I cruise at 24mph and get 10.5 gallons an hour (roughly 2.3 miles a gallon). With an 86 gallon tank under optimal conditions (which is never) my range is 200 miles max and more like 150 miles with some to spare.
Estimating the better fuel efficiency of your 4 stroke and subtracting your reduced tank size....you are probably in the same range.
Fin~S
