If you can port it yourself, the larger outlet will in a nutshell, lower psi #'s a tad, lower outlet temps, which in turn lowers KR from the build up heat it had prior. It's free minus the blower gasket if you already have a dremel or die grinder...takes a couple hours or so...just make sure you check out all the how-to's if you do it...it's pretty straight forward and easy.
Also, DHP's like to run kinda on the rich side...you have upgraded mounts or have the dog bones flipped or running a 180* T-Stat? Do those too if you haven't...super cheap.
If you still have knock on the 3.4" after all of that...get an MPS system if you don't have one and swap the 3.6" on for the winter. It should be fine there.
