Re: SSL-3 vs SSL-4
Until I changed amps, the Hot just didn't have enough highs for me, so wouldn't think it would become ear piercing without some serious EQ. I can see the QP being piercing because of the extra highs. But, it probably depends on your guitar, rig and taste. As you said, they are different, and I like them both.
Another consideration, the QP looks different than the others. This may or may not be a problem for you.
I also like the Custom in a strat for a sort of vintage/hot vibe.