I went back to the previous window over a window, and turned off swapping. Here's why...

Previous setup I was able to see both toons in one window, health, dps, targets etc. When I needed to switch from tank to healer, I would just ALT+TAB and the window. Oddly, when I did the window'd mode and ALT+TAB, there was no ui loading splash screen...so the swap was as instant as I could get.

With the windows side by side, and the instant swap enabled, the 3-4 seconds I have to wait for the ui reload splash window to complete had wiped my toons twice.

Im currently working on a video region with a repeater region overlayed to use the side bars for each toon, and then just operate from one window. I.e. Healers spells are all on the left side of the screen (closest to the group tree), and the tankin specific stuff are on the right action bar. I think Ill have this working tonight.