exhausted :) what system to install?

The tricky part is that it will likely be a little different for each engine setup based on cam selection, headers, etc. Theoretically it's an engineering problem that you could potentially solve, but fluid dynamics and flow can do some weird stuff. You'd want to have the right length between the X and the exhaust ports so that the pulses between banks are timed correctly to give the best scavenging, but it will likely be dependent on engine speed as well, so it would be tuned in combination with a whole system in much the same way that intakes have a rpm range they are best in due to pressures pulses in the runners.

Long story short it's my way of saying there's probably no magic bullet answer and you could likely determine what is best for your system, but it could be a pretty complicated affair. You could trial and error it to see what works best (probably the most realistic answer), but it's also the more expensive way to go.