Just finished downloading it and tried it out for about an hour.
It's noticeably faster than Office 2011, thank god. But it's still not as fast as iWork. For example, I have a document I'm working on in Pages that I export as MS Word (I'm the only Mac user in the company).
It's 42 pages, 7000 words, and includes about 15 screen shots scaled down (it's a software requirements doc):
-Pages scrolls fine without glitching/hiccups. Can zoom in/out without stuttering
-Office 2011 scrolls with massive hiccups, freezes. Zooming in/out makes you overshoot what zoom level you want because of this.
-Office 2016 is somewhere in the middle, but closer to Pages' performance.
Same thing in Excel as well, although Excel 2016 is auto-calcing quite a bit faster than Numbers.
Would I pay for Office 2016? Hell yes. It's much improved. But the beta still has some performance issues.
For reference I'm on a 2014 rMBP, i7, 8GB of RAM, 256GB Flash.