I haven't heard Charlie's car, but as far as my hopped up slant with Dutra Duals, it doesn't sound like a CAR to me at all. When I'm on the highway, it sounds just like the fighter planes in all of those old WWII movies. LOVE it! Don't get me wrong, I like the rumble/roar of a V-8, but you can hear that all day driving around town, from pick-ups to Camaros and Mustangs. A hot slant sounds really good in its own way, and it's UNIQUE. Not many souped-up inline sixes out there.
Just my $.02. Oh, and needless to say I vote for slants in this discussion, 'cause they're fun, they're different, they're semi-economical, and (when properly modified) they're as fast as I need them to be.