As the title says, what size plate would be best? Is too much setback a problem?

We just bought a flightcraft bandit 16 foot ski boat to race here in Aus in the state Pro Stock 80 category. (For 80 mph max boats).
The motor is a 13 spline Evinrude V4 140hp that is getting some performance work done. Cut the heads, offshore exhaust, bigger 225hp carbs, power reeds, low water pick-up etc.
We are currently lookin for a jacking plate. I want to get a 10 inch setback jacking plate as opposed to the more standard 5.5 & 6 inch.
Would the 10 inch be a good choice? Is that too much setback? The hull is a nice race type with a great pad.
Also, what is the standard V4 carb size compared to the 225hp carbs? Are there any other choices in carbs that I could use?