Bullet speed modifying for different weapons isn't possible yet. I discussed it with pasik already as we were working on the sniper since the sniper bullet could be faster.
Some extra health has been considered as well, even though every soldier has only 1 health for now. One shot that hits = death.
We were discussing about special AI units which would need more than one hit to die, something like a miniboss
Movement speed wouldn't be bad, not sure on this if this could be implemented without too much hassle, code-wise.
The difference wouldn't be huge though, like 10-20% difference between fastest movement (SG) and slowest movement (MG240)