First off, thanks for the tip about iStat Menus. I just installed it.
So, I got my MBP 16 a couple of days ago (2.3 i9 8-core / 32GB / 1TB / 5500M w8GB). I was worried about posts I was reading here about fan noise and heat. But so far, I have no complaints there. I haven't done anything super-intensive, and I haven't yet connected it to my Dell U2518D monitor (25" 3840x2160).
I've been using it on my lap in my living room the past couple of days, and it's been very quiet and only started to feel warm when I was using it unplugged for a while and then plugged it in, while using it, to charge the battery. I read here from someone that there was no need to deplete/recharge the battery for maximum life, and that you could (and should) just keep it plugged in when you had the chance, so I've been doing that and the laptop is quiet, and not even warm, and the "System Report" indicates that it isn't charging (while my battery meter continues to show 100%).
I'm not sure what magic they're using, but it does seem like keeping it plugged in (whenever I'm able) may be the way to go.
Mine only gets warm once I kick up Parallels, other than that doing office work via Outlook/Excel/Terminal work and etc so far so good.