I have had both, and can recommend both units for use in RIB's. The HydraDrive in the Yam is fantastic compared with the Yanmar gearbox.
Throttling up from 3200 ( 35 knots ) in the Yanmar gives a real sense of acceleration and 45-50knots soon comes up on the GPS.
Unfortunately the boat with the Yamaha in was much heaver ( 45kn max ) than the Yanmar boat so I cannot compare top speeds, but the Yamaha should give a good turn of speed, 40-45knots ?
The only issue with the Yanmar in the past has been the Bravo 3 leg, which couldn’t cope with the torque from the 300Hp engine. This has been corrected, so we believe (?) with the Bravo 3x leg, which is fitted, on my boat.