Using this for the first time at work today ... trying to stretch it's legs. Running dual monitors (built in screen + external Dell 1080p screen using the Apple USB-C AV media adapter) with a Win10 VM, using Visual Studio, xCode, OneNote, Excel, Outlook, Mail.app, TweetBot, Safari+3 tabs, Pixelmator, and Chrome all while listening / watching a video podcast in the background. Memory pressure is high but still "green".
I'm pretty impressed, no slow downs or lags even when trying to run multiple intensive operations at once (i.e. compiling/building a large project in VS and xCode at the same time.) Using the 2016 rMB in a similar fashion also worked surprisingly well (m5 version), but there was noticeable but manageable UI lag here and there.
Will continue kicking the tires and report back.