While I've yet to drop in my Arrow (so many new mech builds to try so little time, and the hero mech sale hasn't helped) I think tweaking a previous good build to add new tech should work nicely:
LB10X ARROW. Stay healthy in the first half of the match and you'll be a beastly 'Crit-asaurus Rex' for the second half. There's also the
RAC5 version for some rotary goodness.
In my opinion the doubling of the MGs range makes the LMG well worth the 30% damage reduction, though in a more 'intimate' encounter (brawling or dropping in a scouting match) I would take the MGs or find the extra weight for HMGs. Problem is that while back in the day I loved brawling with my AC20 BJ-1, today the Blackjack chassis is a bit too squishy to brawl, especially against a heavier mech. I find trying for 200-300m skirmishes works well and the LMG allows the Arrow to do decent extra damage without closing to brawl.
Another build that I've yet to try but 'should' be decent based on the numbers is
this HPPC ARROW. Use the HPPC to do damage at a distance, then when the battle gets within 250m switch to the MLs and LMGs, adding a PPC shot if you're cold enough. For this build I do have a
HMG version who's low heat 10.56dps inside 80m should really discourage the enemy from getting inside the HPPC's 90m minimum range.