I only run my SA-12 on a modest few hundred (around 300-350) watts. I do have a few high powered amps, but never got round to upgrading my cars charging system to make it feasible to install them.
Hands up, this is more about curiosity. I'm more and SQ person, and even the SA that I have is far too much for what I would want to use everyday .... but then I think; this could be a lot of fun ... and I need to do something with those amps, one of them being a Ground Zero http://www.ground-zero-audio.com/en/products/amplifiers_/gzua-2250dx.html
As for the Sundown's, I wouldn't mind getting my hands on the X-8's. Never tried the SA-8 .. never had the need to what with my SA-12 in hand, but my thinking is 'scaling down from a 12" to an 8" or 2 x 8's, without sacrificing output/fun' In my dreams and I think my limit would be the X or Z 10..... but in the real world the SA-12 scares me enough!
So the likes of the 'Nightshade' and 'Team Series' should only be used at the top end of the scale ... serious competing, is that what you're saying?