Whether your currently rooted HTC EVO wants the official Android 2.2 update (version 3.26.651.6) that hit the airwaves on Monday or the unofficial update (version 3.26.651.3) that was discovered over the weekend, it doesn't have to spend another minute worrying about being locked down by a stock ROM.
Both Froyo builds have been rooted.
I haven't heard of any significant differences between the unofficial and official updates—both seem to have the same features (and bugs)—but since anyone who manually applied the former can't get the latter until HTC puts up signs on how to get "back on the official track," you should probably go for the official version.
The instructions for getting the ROM onto your already-rooted EVO are the same for both builds: reboot into recovery mode, do a full wipe, flash the ROM, reboot into recovery when you see the home screen, flash the radio update, reboot into recovery when you see the home screen again, flash the WiMAX update, and reboot again.
For those who have already applied either version of the update, the wait for being able to root what's currently on your phone continues.