I will alternate between my Mossberg 835 with a cantilever mounted 3X9 scope and my Marlin 512 Slugmaster bolt-action 12 ga., also with a 4X scope and I haven't noticed any drop-off in performance.
The cantilever scope mount barrel is Mossberg brand. Both slug guns shoot every bit as well as I can make them.
"Your fear is 100% dependent on you for it's survival." - Steve Maraboli, Life, the Truth, and Being Free