zuren,
The experts are recommending the 1" poly line from the pole barn because it has much lower frictional pressure losses compared to 5/8" line.
The 1" barely costs more, but it will save you on pump wear and electricity, and should pay out the price difference very quickly.
Also if you are in an area that freezes, it has less chance of accumulating enough water in it to freeze. I had a customer that had constant problems with 3/8" line freezing.
