So all the effect seem really overpowered, and are more suited to a Mark 4/5.

I would say that the Mark II should give +50% movespeed and +10 inventory slots, or have a mod config that lets you set the values.

I am not agree with that since there's no Mark 4 and Mark 5 in my mod. There's only Exoskeleton 1 and Exoskeleton 2, there's no plans for making Mark 3 and etc. Mark 2 is twice powerful than Mark 1, all bonuses are calculated in terms of Electricity it consumes.
With configurable options you will be able to make it unbalanced, that is not designed to be like that. You'll have to adjust the Power it consumes as well.

No I'm saying the current stats make it too overpowered.

I will second the notion of it being overpowered. It's not the matter of power, but of how much speed it gives. Spidertron, 1 reactor, 1 exoskeleton II, 5 red shields and batteries. I could pretty much run up, fire rockets and run away with impunity. Keep moving and I could all but ignore the bugs, occasionally leading them back to my gun line but usually just leaving them behind.