Hi there. So we don’t provide much info since it really depends how XWiki is used so it would be hard to say that for “1000 users” you need to have so much CPU and memory. It would depend on so many things.
However we do indicate some ballpark figures, see https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Installation/#HHardwareandSoftwarerequirements which leads to https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Performances/#HMemory for the memory part (which is the most important).
If you have response time issues due to heavy loads on your XWiki server, you should then look at https://www.xwiki.org/xwiki/bin/view/Documentation/AdminGuide/Performances/ and especially clustering.
FYI we know companies using XWiki and who have over 100K users so what I can tell you is that XWiki can scale (there are some known limits indicated in the performance guide but with workarounds).
Thanks