Better curtains might help. That, and many of us remember what improvements we saw once we tweaked our technique and prep. While you may already have it perfect, as a general rule of thumb, tech and prep leaves much to be desired for most people starting out. For me, if I went back to shaving with a cartridge razor from a straight tomorrow, I think I'd see far better shaves than I remember just based on what I've learned here (grain patterns, prep, use of a brush, quality soaps/creams, After shaves, etc.).
I travel frequently enough that I still have the ol' M3 in the carry-on, and I have definitely noticed that the shave seems to be better now than it was before my epiphany. That said, it's still noticeably inferior than I get with the straight, and the "enjoyment" factor isn't there of course. To address the OP's question, I do strongly believe that, assuming tech & prep are adequate, the straight vastly out-performs the cart on heavier growth.
I Conquered the 2012 Shave Purchase Sabbatical
It really is all James' fault.
(Okay, maybe Owen had something to do with it as well.)
+1 agree with Price. As I tried to get at in an earlier post when OP first asked, straights IMO do out-perform on heavier growth. I feel the multi-blades pull at your beard. If/when blade 1 dulls, it lifts the whisker then to be cut by blade (2,3, 4, etc.). This, IME, means the hair is getting cut below the skin line which for me lead to more chance of ingrown hairs.
Sometimes I wait a couple days in between shaves because it's so much fun when the straight razor effortlessly mows down the extra growth.