Is it worth installing a Imco extension box on a 25 outlaw? Any major speed/performance and handling differences?

Currently running 73 mph with -1 imco shortie and stock 26p B1 prop. (X-dimension is currently 6.25") I could probably get a couple more mph with a labbed prop etc.

I have hydraulic steering which I am going to add to the boat. One reason I am leaning towards a box is to avoid putting additional holes in the transom.
I would like to do a -3 box to get my X-dimension around 4"

I have an IMCO neutral box with and Imco single ram and 280's on my 25 Outlaw. Forget about the speed, the boat rides completely different for the better. If you do a -3 box you'll need a stock lower or space yours back down 1", you'll have to raise the motor too.