Hitters use 1" dowels. It's hard to find a crooked one of those. Those 5/8th's will bend just looking at them.
I tried the 5/8" dowels but under the stress of a swingers' lag pressure they were too whippy, and prone to staying bent. I had to change to 1 1/4". If I use a hitting stroke pattern then I would go down to 1" dowels too.