the trend to put smaller 4st motors is definitely because of the weight difference...the four strokes develop a different power curve to the 2st motors...a mid range 4st will get the hull on the plane and hold it on the plane at lower speeds than the same size 2st as they develop their power at higher revs...when I looked ar repowering my vsea I had to work out power/weight/fuel consumption to suit my hull..i had a 60yammie 2st.same weight as 70 2st..if I went to a 704st I would have added thirty kilo..no more power no more speed only better consumption...I went 90hp 2st..12 kilo heavier.but massive gain in usable power...jurys still out on consumption as I havnt been for decent trip yet but im thinking same or only slightly more as I use heaps less revs now to do a comfortable cruise speed...it leaps out of the hole and doesn't die off the plane on the back of swells in a working sea.....horses for courses is the old saying....my mate just repowered with 135 yammie 2st..he saved $6800 on the 4st he was looking at....that's a lot of fuel you can buy for that saving...if you find a good hull you like try it on the water and see how it performs with the motor that seems underpowered..it may suit your needs...rick