A couple of historical points I seem to remember. There were X10 versions running on SunOS (3.5?), Though I don't know if it was officially supported. X11 early releases were significantly slower than X10 on Sun hardware.

SunView was originally Suntools. The change to SunView brought some improvements in the UI, but mostly in the API.

I can still remember the days of the Sun 1 with the VT100-like keyboard. To a freshman at MIT who had only seen a Radio Shack TRS-80 Color Computer and an Apple II, it was almost undescribable. It was the days of 1MB of RAM on a "personal" machine and a lab-wide pair of 500MB Seagate Eagle hard drives being all you could possibly need.