On average how much speed can be gained with 2" shorter drives? I realize there are other variable's so this is a bit of a generic question, thanks for any info.

Lot of variables. Boat make, step-nonstop, pad-nonpad, length, weight, power, current X dim etc. Just list what your up to and I would imagine someone here on the board has perhaps done so on same boat and will have first hand experience with.

0-5 mph depending on many factors.

Completely depends... My boat gained 2mph buy adding a spacer (opposite of a -2 lower)

The baja 272 seems to lose speed of you vary from the stock length.

Prop shaft 9" below bottom of boat 650hp non step 70 mph at 5600rpm . Just looking for a more.

That is really deep. I would think that would would see some increase from a shorter lower. What boat do you have? Your specifications are too vague for us to give you any real answer, but I do think 9" is extremely deep though.

32' envision , twin 650's

Even with 2" shorties you're still 7". If I were you I would get a set of -3's. You will need to modify your Bravo upper but it can be done. Tinkerer has done this, maybe reach out to him for advice on this.

What kind of speed are you getting now with your current set up?

Poor fish.