My biggest gripe with the Soundsticks is that they only sound good when you're dead-center between them with the satellites aimed perfectly at your ears. Go off axis at all and they begin to sound dull and muffled.
The Z-4s, on the other hand, are far more forgiving in terms of listening position. They also have a more capable sub than the Soundsticks as well as an excellent wired remote.
If you want loud, then the Z-2300s are another set worth considering. These things will rock the house for sure! Just keep in mind that volume isn't everything. The Z-2300s have both thunderous bass and a very pronounced hole in the upper midrange that I feel makes them more suitable to games and movies rather than music.
Of course, the standard disclaimer applies to any speaker discussion. The only way to know what you'll like is to hear them yourself. I guess that's why I've gone through so many sets over the years. 🙂