Well, lessee if'n I can take a stab at this.
First thing is, the ESP changes the handling dynamics of the boat so that handles like a monohull. It's a very impressive ride and people who get that option tend to be very happy with their decision.
Second, Strakes are a way to help get more of the pontoons out of the water, which cuts down on drag. All things being equal, they increase your ability to maintain higher speeds as you load the boat down.
Third, the reason the 3x25 pontoon setup is faster than the ESP is because the ESP is always going to have more metal in contact with the water. More drag means less speed. Either way, you'll greatly increase your load and power capacity.
Finally, your sweet spot question is, as a practical matter, unanswerable. Not because there is no answer but rather because there are too many.
The SINGLE MOST IMPORTANT THING is to figure out how much money you are willing and/or able to spend. You'll find that knowing this answers a lot of questions for you.
Oh, one last thing...
You'd need to check this with Bennington, but if I'm not mistaken, the most popular power plant is the 150hp version of whatever brand you like. The most popular boats are, again... assuming my info is correct are the G & R series, since they encompass the broad middle of the line. I am not sure what the distribution of the Twin-Elliptical vs the 3x25 setup is. Probably not far from even. If I was going to guess where the "sweet spot" is, I'd say a G series with a 3x25 log setup, some carefully selected upgrades and a 150hp engine. Good bang for the buck there.