If anything the longer silencer will give you slightly better bottom end, but not knowing what's in it makes the point rather moot.
By comparison a longer straight pipe will tune to a lower RPM range than a short pipe or megaphone. FI you were running a race bike, you could, a low power engine like the Enfield Idoubt that you would see much of a difference.
Everybody acts like all these pipes on the market are going to vary a lot in performance. The only one I saw affect performance much on an Enfield was the full Goldstar exhaust with the full 1-3/4" exhaust pipe. the stock pipe is sleeved down. the Goldie pipe robbed the engine of a lot of bottom end power. It improved it toward the upper end where nobody rides the engine anyway. If you wanted a race bike, and modified the engine for the extra RPM,it would be the way to go, but on the stock engine, it was a letdown. As for the other silencers, most are better than stock to some varying degree, but nothing to get your panties in a bunch about! The thing you're really buying is the sound you want.
Bare