Shock height - how much makes a difference?

I'm looking at shocks and the best prices I'm seeing are accompanied by the size I'm NOT looking for. If I need a 13 3/4 and I see a deal on 14 1/3, how much of a difference is that going to make? (yes, I know half inch). But I'm basing that on the fact that my current shocks are kinda saggy right now.

does the adjustability of the shocks effect the height at all?

The full spring length does affect bike height, but so does the spring rate of the springs you choose to go on the shock. Also, if the springs are user adjustable that changes the bike height.

I'm looking at that right now on my 750E project bike. At the minimum, the stock shocks (13 1/2" I think) are going to be mounted 2" higher than the stock location, and I'm considering going for 3". That's going to raise the back of the bike 2" to 3" depending on where I decide to mount them. I'll probably just go with the 2" number to avoid the chain hitting the swing arm pivot.

I think I'm just going to have to be real careful and take it up to top speed in stages until I see how stable it's going to be.

I don't think 1/2" to 1" is going to matter all that much (unless you're short and can no longer touch the ground)