I really doubt the friction coefficient (or whatever) between 4" silicone and (any other material) will make a shag of difference to air flow over such short distances at such low pressures.
Silicone will have more "give" for the installer, and the installation... so you won't see so much things vibrating loose, or potentially rubbing on other parts.
So, my unhelpful advice is "whatever's easiest, man"




Reply With Quote