klmken

I am looking at buying a 45' Wellcraft Excaliber (2000) which is almost a 15,000 lb boat. I am looking at repowering a set of tired 502's and was curious what setup would yied the best cruise speed and the least fuel consumptiom (Bravo 3 drives). I looked at a set of stock 502's top put back in but 1800runsnew has a 540 setup that delvers peak torque at 3600 rpm (638 ft/lbs).
Is running at the peak torque point the best way to achieve the best fuel economy or is it somewhat lower on the rpm scale?? I am obviously not looking to make the boat do 80mph but rather get the best mpg bang for the buck...
Thought, suggestions, comments??
Thanks,
Ken