so far I'm finding the exact opposite in REALLY early testing.
I usually have a MIX RMS of around -18 to -24dB. With my old mastering chain I could easily get up to -9dB before it would start to get clippy. With Ozone 5, I can hit -7 to -8 and it still sounds "OK" by some standards. I'll render a master and then analyze everything and find it's REALLY loud with the same characeristics of a less loud ozone 4 master. If I bring it down to around -9 to -10 it's on par with the loudness I got with 4, but it sounds clearer. I'll do more testing today before I jump to 5 for sure, but so far I'm digging it.