I bought a 10K miles Vmax from the second owner, and he or the original owner had removed the OEM plate on each megaphone end, and then drilled a few holes on a larger diameter around the single exhaust discharge. It made things a bit-louder, but I didn't hear anything like someone had punched a rod through the inner baffle area. There was no change in jetting (I cleaned the carbs, and checked them) and VBoost behaved normally.My first Vmax, a '98, had Cobras with punched out baffles. They were ear-bleedingly loud. IIRC, I replaced them with stock mufflers, which I drilled five holes in each exit area for more noise. I don't recall there being a significant change in performance (improvement or otherwise) going back to the stocker. Then I lowsided the bike, and replaced the stock mufflers with some Jardine slipons, and I don't recall any noticeable performance change there, either.
I do ride so I see the oil red light flicker, pretty-much every time it's started, but because of its throttle response, you don't have-to hold it open for long to see the red light, especially in the lower gears.
I've ridden two Cobra 4/4 equipped bikes for acquaintances who wanted my opinion about performance, i.e., "how's she run?" and my report was the same both times.
"Not as-good as a stocker!" I advised them to ditch the Cobras, replacing them with an OEM or another comparable to OEM performance known-quality system, and discover what a VMax was all-about, because "as-of now, you have no-idea of what it can-be."