GW: I've got the 258 with a single F250. Same hull but in a walkaround configuration and a bit more weight.
F250 puts boat up on plane easily. Optimum cruise for me is 4000 rpm which gets me 27 mph with full fuel and I'm getting 3 mpg in calm water. Wide open is 6,000 rpm, running at 42 mph. I usually troll ballyhoo at 1200 rpm, 6 mph and burn about 1.5 gph. I have just over 800 hours on the engine and it has been perfect.
We test rode a 257 with twin 150's. Even better getting up on plane and better accelration from planing speed. However, I needed to run both engines to maintain trolling speed. You could run on one, but the rpm's are such that you actually use more gas. And the planing fuel economy is considerably less than with the F250.
The F250 is smoother (i.e, less vibration) and more quiet at all speeds.
For me, the redundancy of twins didn't outweigh the benefits of the F250.