Editor 6.1 M060, which is currently in QA, is being tested for Windows 8.1 and Webtop 6.8. I'm not certain what Content server versions are supported, but based on previous support, it will be 6.5 and above:
http://support.ptc.com/WCMS/files/165306/en/Arbortext-Software-Compatibility-Matrices-6.1M050.pdf
6.1 M050 is the most recent version of all our products, and supports Webtop 6.7 and server 6.5 and above
Please be sure to note, after our 6.1 stream is completed, we will no longer provide ongoing support and maintenance for Documentum:
http://support.ptc.com/appserver/wcms/standards/freefull.jsp?&im_dbkey=163457&icg_dbkey=222