I just downloaded and installed it yesterday, and it is so slow, development has pretty much ceased.
It takes several seconds just to switch editor panes. If I click on a file, to change to another file, it can take many seconds. Furthermore, it seems that the indexing spinner comes on constantly.
I removed all my DerivedData from Xcode 6, and opened a single, very small, project using ObjectiveC only.
I opened instruments, and loaded Xcode, then waited. After a while, Xcode "hung" on me again... I clicked on a file to change files, and it just never responded. Here is a link to the instuments trace.
http://i.stack.imgur.com/vyuXv.png
I've heard of people having performance issues, but I've never experienced something like this, even with an extremely large project, so I'm at a loss as to what I can do here.
Thanks!