actually quads, according to mat salleh give better part throttle because of the lack of plenum, but because of the lack of plenum also the idle FC will suck. That's why if you look at ITB maps, you will find they idle quite rich 14ish (compared to plenum setup, which can idle at 16+ for better fc in traffic.)
I got so many chances to try it out, but since daily driver.. eh... sayang my engine oh.
any dirt that gets in the engine will get sucked in, and you will lose compression faster due to bore/ring wear.
but power wise, it does seem to be true, because got two similar setup engines, and the only difference on those two engines was ITBs, and the one running the ITBs got 300+hp on engine vs. 290+ on the one running on plenum.
Actually 5 vavles means that intake restriction is less, so with ITB, should have very good midrange power. But since it's also related to tuning, hard to say 100% if 5 valves can indeed make more power than a 4V setup.