Bandit: Okay, I came up with some ideas in the middle of the night- a combination of reading this thread just before bedtime, and that darn prostate
First, I agree with both wwodnthings and ryan50hrl: your idea is overengineered, but sounds like fun, anyway.
Second, I'm not an engineer, and my analytical math and physics peak was sometime during the Nixon administration, so more than a bit rusty.
Anyway, it might make the location of your strut easier if you rule out areas where it won't
work. What's left is where you can locate it. Bear with my example, which I think can be adjusted to suit your situation.
Some assumptions: The strongest support for the extension is if the strut is oriented vertically, with the hinge at the far end of the extension. If the hinge is moved closer to the table, there is more leverage from the weights of the table and outfed wood to push the extension downward. If the struct is angled (not vertical), some of the force is exerted horizontally, which won't provide support- think vectors.
You need to know the distance between the edge of the table and the hinge. You also need to know the lengths between the mounting holes of your strut 1) fully compressed and 2) fully extended. Think of the strut as a stick of variable length, but with short and long limits.
Let's say your extension goes out 18", and the strut compresses to 12" and extends to 24". One end of the strut is the hinge at the end of the extension, and you want to mount the other end (the "pivot") somewhere near or along the side of the saw. The pivot location has to be such that the distance between it and the hinge is at least 12" for every point the hinge travels in the arc as you move the table from horizontal (up) to vertical (down).
In the first drawing, the outer arc is the path the hinge travels, and the red hatched area is all within 12" of the hinge. If the pivot is located in the red ("too short") region, at some point the extension will jam, because the strut can't be compressed any more than to 12".
The area where it's okay to mount the pivot is anywhere in the clear area near where the table and extension meet, since all points there are at least 12" from the hinge at all times. The lowest point is the best, since it makes the strut closest to vertical.
Now, let's say you want to locate the pivot away from the side of the saw, say by some sort of outrigger, as in the second drawing. In this situation, you need to make sure that the pivot is at least 12" from the hinge; if it's in the "red zone" the extension will again jam at some point in lowering.
You also need to make sure that at no point is the distance between hinge and pivot longer than the full length of the extended strut (24" in the example). The arcs show the limits from the extremes of the hinge- fully up and fully down. Any point in the green hatched area ("too long") is farther than 24" from where the hinge point can be.
So, the okay region to locate the pivot here is the clear triangle between red (too short) and green (too long). I drew the strut where it's most nearly vertical. By the way, with this orientation, you'd need to make a slot in the extension to allow it to pass by the strut as you raise and lower it.
Sorry about the long explanation- I hope it makes some sense, and that it avoids some hit or miss construction. It's easier redo mistakes on paper than in the shop.