My current system can handle huge armies in M2TW, but I use the normal size because I don't like having to waste time flying the camera around the battlefield to see what's going on. With the current RTW/M2TW camera and order interface, it just takes longer to maintain situational awareness and command your units with huge armies. I tend to spend more time zoomed way out, and that's basically a waste of all the low-level combat animations.

If Empire supports even larger armies, I hope they're revamping the UI for camera control and unit orders. The current design is a bit clumsy, and I don't think it's been updated since Rome.