Just read the whole thread and looked up saw specs.
At 5.3HP Your stock 372 will barely notice pulling a 18" bar and chain setup!
... That 18" bar is going to be fun on there. There is literally not enough cutters on that loop to slow that 72 down. It's gonna feel like a semi race saw...
Yes . I think just muffler mod. And then I going to run it for a while. Keep sharp chain on it and let it work. Needs to earn it's keep before any other mods.
It certainly is not a commonly recommendable suggestion, but the chain I run on my PS-7900 is more aggressive then it should be.
Instead of the recommended .020-.025" the rakers are down to about .035" and it is awesome in strong wood.
I do not recommend this for limbing though as it makes a rough cutting experience, but will work in a pinch.
I use Dolmar/Oregon round filed chisel chains, 3/8", .058", 20"/72DL, and they handle the additional bite very well.
NOTE:
When both my PS-6400 & PS-7900 wear chains with rakers set to recommended specs on their 20" bars, there is almost no noticeable difference in form of cutting speed between them (fresh oak, beech, cherry, hornbeam).
True, the PS-7900 can be dogged in really hard forcing her through the cuts - but that is not how a saw should be used anyway.
I mention this only to give an example of power to bar length behavior.
Your 372's 5.3HP will be more then You can take advantage of on a 18" B&C setup.
Lowering the chains rakers
a little bit might give You the desired "wow" effect You are hoping for without modifying the saw.
Dolmar PS-6400 = 64cc , 4.8HP
Dolmar PS-7900 = 78.5cc , 6.3HP
Husqvarna 372XP = 70.7cc , 5.3HP
DISCLAIMER:
Don't go crazy on the rakers!
If You lower them much more then ~.040" the cutters will take too big a bite causing Your saw to constantly bog down and You will have rendered Your chain unusable.
You can try "playing" with raker heights on an old chain, 2/3 or 3/4 worn, that way You won't mess up a new chain!