That was only part of the bug-fix. Making springs not stretch hinges is fine by me, since hinges are supposed to be solid. If you give the spring any leverage on the hinge, it will go though.
The other part of the bug fix that eliminated raunits was that springs would change their strength depending on their angle. That has been eliminated too.
Perhaps they are the right sizes relative to each other, but I agree on them all being too small. However, despite being too small, they are still too big to all be found with any ease.
It's the position, not the speed. Position values only have so many digits, and when they're gigantically huge (far away from the origin, which is at the center of the start screen on a new scene or when you click "default view"), they lose some accuracy. Stuff gets screwed up because of that.
Motor speed is too high. It reaches ungodly speeds when spun in midair, and that's why it freaks out. There is no need for it to be that high. There are also better ways to lean, IMO.
You can significantly reduce the lag by selecting the treads and transforming the links to circles. They are very round polygons in the scene (I suspect you rescaled them into slightly warped shapes), and polygons usually have several times as many contacts as circles and boxes do.
On the same train of thought, you should transform the round polygons in the gun to circles, and you should transform the square polygon into a box. This will give much more predictable shots. They will fire regularly and only one at a time, eliminating their tendency to destroy each other on spawn. Remember that onCollide scripts are called with every contact. Also, that gun works and looks suspiciously like my recharging plasma blaster. I have a feeling that rusinventor gave you a (highly) modified version of my gun, not entirely his own creation.
You can cut down lag a lot with Transform to Circle and Transform to Box in other areas too. I would also suggest changing the bridge to a chain of a smaller number of longer boxes. Fewer hinges and geometries that way.