[kevinp]

I don't know the absolute answer to this question, all I can give you is my experience. The largest map
I have made 1:1 scale is 595 x 465 miles. All my attempts to make it bigger failed.

I'm not sure what you mean by" practical" size for the brief map. Are you concerned about file size or do you want a brief map that has enough detail in it to be of practical use in finding the target.

Here's my biggest map. I had to move Scotland about 60 miles closer to Norway to get it to load.