Currently, the assault spidertron MK2 feels completely unbalanced given that a player or set of turrets can fire faster than it. I did a little testing on how to rebalance it, and the best tweak I could find that didn't completely overpower it would be to set it's chain_shooting_cooldown_modifier = 2.0 or 2.5 in entity.lua and and cooldown = 2 in gun.lua depending on just how powerful you want it. Personally I feel that any specialized MK2 should be quite powerful in it's chosen field, so I prefer the 2.5.
Take of this what you will.
EDIT: After more experimenting with the MK2s, I think they need a buff across the board in their respective areas.