I have been researching this for a long time and thought maybe we could use a post just for compiling data. Most people may no how to check it but if you do not here is how I do it. Get the outdrive as level to the boat as possible. Use a 4' level or strait edge and lay it on the bottom off the boat. Measure the distance from the top of the level to the propshaft centerline. I will post my boat and a couple other friends boats to get it started. If anyone has made any changes post the height before and after and if it helped speed or handling.
I just noticed we are getting great responses, maybe add your prop pitch and type, top speed ect... like some of the guys have done.

This is my boat with a Bravo 1 outdrive the depth is deep at 8". I am currently using a Mirage prop. I have tried a 25 pitch mirage lab finnish @ 4900 RPM and 23 pitch mirage (non-lab) @ 5400 RPM both have similar speed 69-70 on GPS. I may lab finnish the 23 and see what that does. Running a 489 stroker engine with 500HP.

This is a friends boat with a Bravo X drive at 6.5". He uses a Mirage prop and plains off with no problem

This is a friends boat with a Bravo X drive at 5.5", he uses a bravo 1 26 pitch prop and has not tried anything else.

Mine are around the 3" neighborhood... I have boxes too.

I run 32 pitch maximus's......those seem to work good.

8" ,I tried a 2" shorty last year picked up 3mph, bought a 1" spacer and during testing the lower gears let loose and wasted the housing. im running the stock length for now ,just bought a new 2" lower to try again next year.
I'm a low tech drive guy.
800hp . 32p bravo none lab

I run the propshaft 3.5" below the keel spinning a 30 pitch P5x doing 92.5 mph with 730 Whipplecharged horsepower.

Always lookin for more,

Chris

I went from a propsheft to bottom height of 3" to 1" and gained 2mph on GPS. i allready have a -3 IMCO and am 1/4" from the swim platform or would put the propshaft higher. I am running the ITS standoff. The boat rus 90 on GPS. Handles and planes great.

Donzi classic 18, 5" below with -2" shorty labbed repitched 29 to 28 pitch M+ runs 72-73 on gps stock mx 6.2.

I assume you were at 7" before the shortie. What gains did you see with the shortie drive?