I've got a 1+4 setup over 2 PCs and, so, can't PiP all 5.
What I've gone with is 1 on my main PC, max res/graphics etc.
4 on the second PC in a 1&3 formation (both screens are 1920x1200).
I use Kavoom, virtual Keyboard/Mouse switch, to "share" one mouse/keyboard between the 2 PCs... simply move off the right hand edge of PC1 and the mouse+keyboard "move" over to the second PC.

On the second PC, I can then PiP to the larger of the 4 windows.

So, main dies, I hit F7 and #2 char becomes the new main and if he dies, F8 and #3 becomes the new main and switches to the larger window.

Works well... you barely notice that you're not on 1 PC, to be honest