Our user environment is, and is likely to remain, 8.5.3. There is a possibility we'll be doing a server upgrade to 9.0.1 so I know I need to install and use the 9.0.1 admin client. I believe this also pushes me to the 9.0.1 designer client as well.
It looks like I'd be safe doing design work with a 9.0.1 designer but wanted to bounce it off the group just to make sure.
Thanks for your feedback.