I had a really nice after market system at one time that was pretty damned good. It had plenty of spl without breaking up or clipping and a bona fide 2 x 100W @8ohm McIntosh amplifier for my front speakers (Boston Acoustics, separates so I could mount the tweeters higher) and a Zapco mono amp (1 x 100W @8ohm) driving a 10" dual voice coil driver (TSW I believe) wired in parallel. I built a simple 1 cu ft sealed box for it, used fleck stone to finish and it actually looked pretty cool. No sanding or anything.
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That's not actually it, but looks a lot like it. You gotta spend some money (as with all things audio), but you can still put together a really kickass system that will rival or better most stock systems. I know OEM car audio has gotten better by leaps and bounds, but as far as clarity, very well integrated bass and overall performance at even high spl. I haven't heard a car stereo that sounded better to me than mine, but I have to admit it's been about 13-15 years or so since I had it to listen to. I've heard a lot more powerful, but mine sounded just, sweet.
There were times when I wish I had a little more bass, but for my style of music my little sub worked very well, and the BA speakers with the McIntosh were pretty sweet too. IIRC that TSW speaker had very good sensitivity and didn't need a ton of power to hit good spl and the Zapco never got ridiculously hot. I ran the voice coils in parallel to it so I was guessing I was getting ~ 180w @4ohm. Definitely not a ground pounder, but that's not what I was going for. I wasn't trying to rock out the guy next to me, but I had plenty enough to drown him out!
All of this is, IME, IMO and YMMV, of course.