I used 1" for my whole sprinkler system. For a 250 foot run, I'd certainly
want something bigger. You'd get better pressure.

If the water pressure coming from the main is significantly higher than
what the sprinkling system will use, then run high-pressure along the long
run, and put a regulator at the other end of it. In my area, the water
pressure fluctuates between 95 and 105 PSI, so it wouldn't be a problem for
me - but I realize that not everyone else is so lucky. : )

Some people don't even use a regulator on their sprinkler systems, they
just hook 12 or more heads on a single circuit. With all of that flow and
the restriction of 3/4" pipes, it ends up dropping the pressure enough that
heads don't blow up... but the water hammer is unbelievable!

steve