IME, usually you care more about latency than throughput for normal interactions, and there is a noticeable difference between the slowest ones, and the fastest ones, but I've tried a lot of terminal emulators, and any of the ones that put some effort into performance are plenty fast enough.

However, there is one case when throughput matters: when an application has a lot of output. But then the problem isn't the speed that it displays the text, it's going by too fast to read anyway, the problem is that the application can be slowed down by blocking on writing to stdout when the buffer is full. And honestly, the best approach in that case is probably not to actually render all the text, but send most of the output straight to the scrollback buffer, and only render some of the frames.