I have made the crossing in a small Boston Whaler several times. I used a 13' Whaler with a 35 Johnson and 18 gallon under-seat tank, going from Lake Worth Inlet to West End. We always traveled in company of other boats, and we only burned about 3-4 gallons per hour.
I never ran into bad weather going over in the early morning, but we did give in to good sense in bad weather, and have a friend's 36' Tiara Pursuit tow the boat back a couple of times while we rode with him in comfort.
At the time, my other two boats were a 17' Cruise Boat center consloe with a 55hp Evinrude, (built as strongly as a floating potato chip), and a Slickcraft SS160 with a 140 Mercury. I would NEVER take the Cruise Boat for fear some 2' wave would break it in half. However, the Slickcraft also made the crossing twice, but we had minimal fuel reserves with only an 18 gallon tank and burning 6 to 7 gallons per hour at a 30-35 mph cruise.
JFTR, my fastest crossing was as a passenger in a 30' Formula 302 and 45 minutes buoy to buoy. The distance is 54 miles. Equipped with twin 830hp Gale Banks motors and Arneson drives, we ran over 70 mph for most of the way in almost glassy water, and had to slow to about 55-60 on the far side of the Stream because of a cross-chop. That was back in the days when I had delusions of making a name for myself as a throttleman.
We did not beat the record which is what we were trying to do. The record, which as far as I know still stands for v-hulls, was set in 1984, and is 40 minutes flat at an average speed of 81 mph, set by Rocky Aoki with Steve Stepp at the throttles in a Gulfwind Marine 30' Velocity with with Mercruiser power.
Back in '01 or '02 I heard rumors of a just barely sub-100 mph crossing by a 45' Cougar unlimited cat.
I'm getting older, but I still love speed on the water.
__________________
Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury