From my Point of View I thought it would'nt make a difference how the mixes are layed out.
I thought just the Resolution of the Sources and Fx Adding makes something about the performance.
I don't want to play out a Video in native Resolution 3072 x 768, it's more to have the possibility to run three Videos on the different mixes and add a keyed Image as canvas over all the Videos.
Playing Out Videos as tryptichons I normally use resolutions like 1800 x 400.
The 3072 x ..... was just for explanation about the Mix differences
Best
Rolf
www.chaoscenter.net