Ok, all things being equal (which they almost never are), you will almost always get smoother transitions from a 3 way cabinet than you will from a 2 way cabinet. The technical reason lies in the way that the high frequency horn drivers are constructed. HF compression drivers have a diaphragm, which is usually 3/4" to 2" in diameter. The softest material this will ever be made from is a stiff Mylar plastic, and the hardest material, titanium, with several (many?) other materials having been tried & used as well. This is excellent for true high frequencies, but can sound a bit harsh for mids - generally speaking, you want the mass of the driver to be in sync with the frequencies it is producing, so a large 15" driver transitioning directly to a tiny 1.5" (ish) driver is technically sub optimal. The human voice falls mostly in the mid range of frequencies, so having a 5" to 8" mid range driver can help to smooth this out, especially when the low frequency driver is a 15".
(Side note, in my opinion, this is why modern DSP optimized active cabinets are awesome: the engineers can program the DSP to compensate the amplifier & driver response curves to really minimize the impact of only having a HF & LF driver, whereas in the old days you'd need a spectrum analyzer, a graphic EQ & a bunch of time to really sort this out).
Anyway, in many cases when using pre-recorded music, the difference will be subtle. I don't think the difference is going to jump out & smack you in the head (or ears). If I had to guess (since I've never personally auditioned either of these speakers), I would say that you would hear it clearly in jazz, whereas it might be close to imperceptible in EDM (nothing against EDM, BTW, I love it too).
Having said that, if you don't mind carrying around the 85lbs !! weight of the JBL 3 ways (JBL SRX 835p), I think you would enjoy the sound they can produce for you at your gigs. I suspect that they would be sonically similar to the QSC KW153, a DSP active cabinet that I am familiar with and really like.
