After I get my 5-box setup, I'll probably play around with this a bit.

My idea right now is to eliminate the party frames from each of the other
four clients, and instead enlarging/rearranging the party frame on my
"main" client's second monitor so they are visually related to the
corresponding neighboring monitors.

[O][M][O]
[O][X][O]

M - main client
X - main client's second monitor
O - other clients with no party frames

I want to create a centralized information HUD that is large and clear
enough to be read with peripheral vision (which means the information will
be mostly graphical instead of text based).

There's even the possibility of the other clients sending info over the
party-ui channel to feed the main client's information center.