The F100 is only around 10kg less in weight than the DF140 Suzuki engine if I remember right.
I don't think you'd have any speed loss issues on a 5.5m rib with the 140 Suzuki somehow, and also since the boat is smaller and no doubt lighter, you'd probably get better mpl than I do by some way.
I've had no mechanical problems with my engine at all to date. During the first service, the engine wouldn't give the local Suzuki dealer any information without a software upgrade, which did take a long time to get right, but was fixed in the end, and showed no problems at all.
Fuel consumption is damn good, and the engine itself is dead quiet when idling, and really not much noisier when cruising, or even at WOT. As I pasted in another thread, goto www.suzukimarine.com
for an idea of performance stats and fuel useage data.