I normally go up to 320 grit, which is the highest grit I presently have on hand for my random orbit sander.
I have only made one end grain board. I do not recall using any different process for sanding with the ROS.
With a face grain board, there is typically a portion where the end grain is exposed. I do sometimes sand this end grain by hand to 400 or 600 grit. Gives a smoother surface and can enhance the appearance of the grain.
Take a look at a recent post by Phind's where he shows his new end grain samples for his excellent wood identification site.
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