Be aware that if you exceed the coast gaurd ratings for horse power that you will probably void any insurance you may have in an accident and you will have a hard time finding a reputable dealer that will put a motor on there that is bigger that CG specs.
If you are looking for more speed with a bigger motor on an Arima you should probably look at a different boat. These boats are great at 30 to 35mph max and 25 to 30 cruising. I don't think hanging more horses on it will give you a great deal better preformance and may make the boat unstable.