So this is what I have come up with for this variant. I quite like the crabs up until now, but I still need to try them out a lot more. I do think however, that this one is quite good, since its fast, but still carries a nice amount of firepower.
I've been running with a similar build utilizing the top XL350 engine. It's the one crab that can equip a 350 so might as well do so. 1 LL in each arm and 3 MLs in the torso. Good at running around and flanking at range, get off a few shots, reposition, repeat. The legs are a little weak though, so do be mindful of that as people love going for the legs on the crab mechs if you're not careful. The new quirks also give this guy a -15% Standard Laser Duration which is nice.