I've just had my DF140 replaced with a DF150 by Ribcraft despite their reservations. it's a huge improvement and if anything appears to make the boat more stable at speed (possibly due to the greater size of leg). It accelerates like a rocket and has gained about 5kn. I don't know about the economy. I was expecting a bit of a trade off with the handling but if anything it appears less flighty going over large waves (even after taking air).
The df140 has been great on the 10hrs we've put on it before winter, very good on fuel and excellent top end. Could probably do with the extra torque of the 150 for acceleration but difficult to tell yet though as it's only just running in.
