I am currently repowering my Scarab Excel 31' with a pair of 525SCs. Considering the addition of extention boxes. How much additional speed will they provide?

The boat is a 1990 with a V pad bottom, no steps or notch and 23 degree deadrise. It is a heavy boat by today's standards. Factory claims it weighs 7,300 lbs dry (likely more). In addition, the drives are deep. The propshaft centerlines are 9" below the hull running surface directly ahead of each drive. I've been told this should be closer to 4" or 5" below the hull for better speed.

I have studied both the IMCO and Stellings options. I like the IMCO with the 3" rise but not sure if I want to have flame arrestors sticking through my hatch! I like the fact that the Stellings boxes can lift the drives by 2" but am concerned about the maintenance of the drive shaft/u-joint. Have also read that this system is hard on drives with the elimination of the coupler. True?

Does the added weight of the boxes affect performance? Would the boxes still improve performance if I use a neutral set-back?

I will also be installing a new pair of Bravo XRs. Also have a pair of Imco shorties -2". Not sure which way to go on this project. Appreciate any ideas you have! Thank you, Jeff Stone