I’m considering upgrading my speakers internal wiring

Curiosity killed the cat...luckily they have 9 lives.

I'd say scratch that curiosity itch - audiophile fun and likely better than a lifetime of wondering.  Seems like you can go back to the original wiring if desired.

Many years ago I re-wired a pair of speakers with what I thought was better wire. I loved those speakers, but after re-wiring them they sounded sufficiently different that I was never happy with them and I ended up selling them. Not only did they sound worse, I was constantly second guessing whether this was the way they were intended to sound. I have always regretted what I did to those speakers and wish I still had them in their original form.

You say:

I have a beautiful pair for PBN M1!5 in a Black finish which I love and sound incredible.

If you love them and they sound incredible, why on earth would you want to modify them? It is hard enough in this endless obsessive pursuit that we all subject ourselves to, to find something we love. In that rare moment when you do, try not to kill it. Even if you succeed in making it sound "better", it will still sound different, and that itself will be enough to drive you crazy. If you have an itch to scratch, buy some exotic power cable but please leave the speakers alone.

Thanks for all the input. I’m still on the fence. Also the fact that they sound great nor… upgrading the final 2 feet to the speakers themselves should Improve the sound further. 
Kenny I did not pay 18k for these. Reach out to Peter himself and get pricing. They’re worth every penny 

You’ve gotten great advice.  I’d call and talk to Peter, in this hobby owners / builders, designers will often give candid, great advice on their products.  Not across the board but more often than in most industries.  If you have that itch, you will always want to scratch it, if you keep the old wire, take pictures, you can always reinstall the original wire if you don’t like the upgrade.  

The downsides are if Peter voiced the speaker not off of what the components cost but what sounded the best with his design and synergy with the other components, design, I wouldn’t mess around with trying to make the speakers “better”.  Peter, if he’s honest can point you in the right direction.