Office 2011 seems mostly OK for me with El Capitan (I don't use Outlook so haven't been affected by those problems), but Word seems sluggish on some documents, with spinning beach ball or 'application unresponsive" messages. I haven't worked out yet what the problem is, it is not as simple as document size or the number of embedded images. I've been using it for the past few weeks, with documents up to 100 pages or so. El Capitan has done nothing to improve the experience of opening large Word documents in Office 2011...
Reliability of Office 2011 online with Onedrive is variable for me - I use this quite a lot for large (>100 pages, lots of pictures) collaborative documents - it worked beautifully for a while last year, I lost data in Spring 2015 (and discovered a phenomenon whereby if my Windows-based collaborators edited in the browser instead of locally in Word this would reproducibly crash my Mac-based session in Word), and now it is flaky, often crashing/freezing.
Crashes in Word when using OneDrive seem to also bring down Powerpoint quite often or vice versa (e.g. when cutting and pasting figures from slides into Word for a report).