Most of my saws are stone stock, and I feel no need to modify them in any way. My Husqvarna 262XP and 268XP are excellent in stock form. My "go to" saw is the 55 Husqvarna, as I cut a lot of tops these days. It's a closed port version, and has plenty of high rpm power and torque for the size of the saw, never saw a need to mod it in any way.
The Echo CS-510 was a TURD without opening up the muffler, so some saws respond well to modifications, or need some help. I'm thinking also that at least half of my saws are early models, and may not have been subject to emissions or had restrictive mufflers on them anyhow?.....Cliff