Join Date: Aug 2009
Location: Portland, Oregon
You have to remember that Astartes armor isn't light. The marine is insanely dense.
I don't think any small booster is going to get a marine very far or increase his speed in any serious way. Hence why they need those honky massive jetpacks to get them anywhere.
As for what minor modification...I'd say some sort of ammo backpack or satchel. Marines carry just a handful of magazines. If they could carry, say, 20 magazines, their tactical flexibility would go up considerably, I think.
That or something akin to Terminator gear where they can get a 360 view around them at all times via their helmet feed.