[rovolo]

I'm not sure what you mean by this. The Eastern Interconnection is far larger than the Texas Interconnection and it's connected via AC. Are you saying that the Eastern Interconnection has inefficiencies due to its size? Or are you saying that the Eastern Interconnection isn't fully synchronized somehow?

I tried reading this IEEE article about the time the Eastern and Western Interconnections were connected into a synchronous system (1967-1975) to learn more about the difficulties with scaling interconnections. It mentioned frequency oscillations causing voltage variations close to the East-West connection (p11), which sounds like the issue you're describing. If that is the issue though, then Texas isn't the size limit for a grid because the Eastern and Western grids exist and are far larger.

https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8594689

[bluGill]

About is doing a lot of heavy lifting here. Yes you can go bigger than Texas size, but Texas is still big enough.