I don’t think TECO is inherently bad for this size of file. What might be tough is, if anything were compute-bound, and the processor were loaded down with other jobs, you could have the usual timeshare-related problems. If you wanted to look at a chunk of text, it would be a problem to send it to your TTY.

If you were using a KA10 variant, your process could get evicted pretty easily because the core memory requirements of all the running jobs had to be less than 256K words. The variants with paging would have a more efficient method for virtual memory.

Compile times would be affected by the same issues.