Well, the moratorium period finally ended on Record Sheets: 3150 so that means there's two new variants to talk about, and they're both trying to put a similar spin on the Penetrator.
The PTR-7D showed up in TRO 3150: New Tech New Upgrades all the way back in 2013, but we didn't get the actual record sheet for it until this year, while the PTR-8D appeared in Recognition Guide 27. Both use Reflective Armor to give themselves an advantage against enemy lasers and PPCs (and plasma and flamers) but diverge from there.
The 7D swaps out the ER Larges for a pair of Snub-Nose PPCs and uses Actuator Enhancement Systems to improve their accuracy. The six medium pulse lasers in the torso are untouched, and it saves weight with an XL Gyro at the expense of crit vulnerability in the center torso.
The 8D uses Reengineered Large Lasers in the arms for the same accuracy as the AES-enhanced Snub noses, but with more damage at medium and long range and, of course, the ability to punch through Reflective, FL, or Hardened armor on enemy mechs. It switches the pulses over to standard medium lasers and swaps the AMS for a LAMS, eliminating ammo dependency at the expense of the LAMS's high heat burden. To help with that, it's got an extra double heatsink (a total of 26 dissipation compared to 24 on the stock or 7D) and a single coolant pod as an emergency cool-down measure. Durability is improved thanks to mounting more armor than the 7D and having a Compact Gyro instead of an XL.
Me, I'm dubious about putting fragile Reflective Armor on a mech that's slow and only mounts short-to-medium range weaponry. I think the 8D does it a bit better, but I'd be real nervous about anyone getting into slapping range with it, and most of the things it fights will be close to that by the time it can start shooting.