Generally you don't get much of an option about selecting the diameter of a propeller in a particular line of standard propellers. The manufacturer selects the diameter that works well with the pitch in his various lines of propellers.
Diameter becomes a factor in propeller selection when the propeller diameter is larger than the propeller aperture--that won't work. Other than that, you generally are going to select a propeller by pitch and the propeller manufacturer will work out the diameter.
Because stainless steel propellers in general are expensive, and specifically the ENERTIA propeller--made from a
Rearden metal--is even more expensive, you should be careful about buying an ENERTIA propeller if you cannot sea-trial the propeller and return it, should it not work out for you.
Also, you might consider the ENERTIA ECO. The ENERTIA ECO is a derivative propeller designed to improve fuel economy.
Generally, if improved acceleration is a goal, trying a lower pitch will help. If you want to simultaneously improve top speed at full throttle and improve acceleration, you need a miracle propeller.
If the 210 VENTURA was set up from the factory with the OptiMax 225, then Boston Whaler usually has tested plenty of Mercury propellers and selected a good one. You should consult the boat test data published by Boston Whaler to see what the OEM propeller selection was, if your boat is not running the OEM propeller. Boston Whaler's test results can be a good guide for propeller selection.