Being a small operation, I usually mow 8 laps around the bigger fields and get that baled and out of the way. This usually results in about 6 to 8 acres of hay to put up. I then continue to break the field in the 7 to 10 acre chunks. This allows me to make sure I don't have so much hay on the ground that I can't get it all in before the rain gets here.
On the smaller fields (5 or 6 acres), I'll mow 6 laps for the headlands and then finish the rest by just going back and forth. By the time you get the headlands done on these fields there isn't much difference in making 90 or 180 degree turns. The headlands are usually short enough that you can just mow from the outside toward the center and drive the width between.
Now that I use a NH stacker wagon, I might up the number of acres. Although it is kind of nice to do easily do 600 to 800 bales in a day and be sitting on the front porch with a cold drink by 5:30 or so!
One other thing to keep in mind about turning is what type of pto shaft setup you have. If you don't have a CV style drive line, tight turns can be difficult.