Running passive and set gains by DMM to 125WRMS on a 1K@0dB tone. My tweeter is mounted directly above my woofer and behind the door card. This tweet is EXTREMELY forgiving of less-than-optimal installation, but I did need a little TA to keep things from getting ringy.
Trust me, I'm a musician and I'm an asshole when it comes to accurate-sounding drums and guitars, two things which I believe are some of the hardest for CA speakers to accurately reproduce. When you can hear the finger come off when individual strings are plucked or that sustained fadeaway of a properly-done crash cymbal, it all feels worth it.
TBH, I would avoid supertweets like the plague if you're looking for accuracy. They're really just meant to keep up with super-loud systems, not accurate reproduction. Definitely consider the BG Neo3. It's a planar tweet which uses an entirely different technique towards projecting sound. You should get a much better sense of airiness and space in the recording when you listen to them, something I'm sure you'll appreciate. Only downside is they're about 50 each, but they are sealed-back and should go into the a-pillars with a small amount of fiberglass work.