Well the X65 stick doesn't move.. it measures how much force you're applying to determine 'virtual movement' of the stick. I haven't used one, but because it's so different you may want to consider trying one before you buy it if at all possible.
The G940 is a Force Feedback stick. This is what I am currently using. While the Force Feedback is top-notch the stick itself is still quirky. The only reason I bought it is because I found a sale on Amazon for $200 shipped brand new. What do I mean by quirky? Well for the most part it's a nice piece of hardware, but it suffers from a condition that we call "The Reversal Bug".
Basically, if you move any axis in one direction, and then slowly reverse its direction, it has no effect for a short while and then it 'jumps' electronically to make up for that amount of movement with no change. The amount of this reversal bug varies between 1.2% of movement to 5% or more depending on the axis. This makes it difficult to 'fine tune' your aim, throttle setting, trims, etc.
The good news is that after many months and two software updates that were 'supposed' to fix the problem and didn't, on the Logitech message boards they've finally devoted an engineer to work with us to help develop a fix, and they have given us confirmation that this reversal bug CAN be fixed with a Firmware update, and are working on a Beta Firmware as a stop-gap until an official release can be made... so hopefully this will all finally be a non-issue in the very near future.
This "reversal" bug is like this. Lets say full 'up' is ZERO and full 'down' is 100. As you move the stick from up to down you'd see 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16 and then at this point you decide to reverse the direction. It would do this: 16,16,16,16,12,11,10,9 and if you reverse the direction again you'd see 9,9,9,9,14,15,16. Basically, you're forced to 'overcompensate' any time you need to change the direction of any axis.
In case you're curious, I made a youtube video of this here:
http://www.youtube.com/watch?v=xiwyBM7PXEoBut.. like I said otherwise it's an AWESOME stick. I don't regret my purchase at all and hopefully this one issue will soon be a thing of the past.