Is this something that could easily be addressed?
No, both of these have been optimized as far as possible. These are as fast as I can make them. In fact, they will likely be slower in future when I change mIRC's display routines to use more modern Unicode APIs, which are far more involved/complex. Apart from that, features like /loadbuf and /filter expect to handle large numbers of lines, so their line loading methods are very different. Such methods cannot be applied to /aline or /echo.
