I've had a few days to live with the recent changes (out with the Focal ISU200 woofer/tweeter as well as the Kicker L7T8) installing the Dayton SIG180-4, the Hertz MP25.3 and Skar VD-8 D4.
I'll start with the sub, I'm pleasantly surprised, it's low end response is fuller. I'll have to take some frequency measurements at some point but subjectively there's an extra octave down there. The tradeoff is some punch, it doesn't have the impact of the Kicker or especially the new Highland's dual 8".
I could easily live with this, I think this subwoofer works better with the stock enclosure than the kicker. There are different resonances in the car and new panels have come to life. I went with the dual 4 ohm version so that I could find someone with a LR/Performance to try this with the stock amp. The kicker amp still provides plenty of power at 2 ohms (dual 4 ohm coils in parallel) but I suspect the dual 2 ohm would work better with the Kicker 500.1 or Skar 5001D for those who are upgrading a RWD.
Conclusion on the sub: The kicker doesn't provide the same value, if you're on a budget, go with the Skar. If you're not on a budget but prefer low bass vs punchy bass, again go with the Skar. I'll need more time, but subjectively the Kicker is more articulate, the bass is cleaner and tighter, but the Skar is quite enjoyable no question about it.
Tweeters, I've talked about this previously and knew that I prefer the Hertz MP25.3 tweeter to the Focal tweeter. Much of that is my personal preference, the Hertz is just smoother less fatiguing and I'm not exactly sure how to describe it, but the Hertz just sounds better, so unlike the sub where I could live with either, my taste just doesn't jive with the focal. If you like brighter tweeters, the focal might be for you. I have some Dayton tweeters to try, perhaps there's something a bit more budget friendly that performs like the Hertz.
Door woofers, the Dayton SIG180-4 reminds me of the Hertz woofer, I'll have to swap the Hertz back in for a more back to back comparison but as a direct comparison to the Focal, I like the Dayton better. It's not as night and day as the tweeters, but the midbass is just a bit nicer, I'll have to do another comparison to see how they work with the Kicker sub. The bass is just everywhere, it's less identifiable as far as proximity compared to the Focal/Kicker. As a whole the system is more well rounded (Scan Speak 10F's in the dash/rear doors, plus the Dayton/Hertz/Skar I've been talking about). Given the price, just like the Skar, the Focal woofer isn't worth the premium, and the Hertz woofer might not be either, I'll have to swap the Hertz woofer back in after I've gotten used to the Dayton for a month or so.
That's not to say the Focal set is bad, it's a lot better than the stock speakers, there's just more room for improvement, the universal line is one of Focals lowest lines so I can't fault it.
I could live with this system as it is today and be incredibly happy.
I'll get the Skar amp in soon and see how it pairs with the Skar sub. If those work well together it might be a great budget option without significant compromise.