To win 99% of the time, other 1% sometimes for information if it isn't costing too much (especially if a cash game where it can help to adjust better to a certain player).
Based on small sample of my getting back in the game recently, about 4k hands accross 3 different limits so very small sample lol, think im 57% to showdown (or it might have been wsd) .... not really played enough to do much analyzing of my stats yet.
But basically main purpose of why you want to go to showdown is to win, and how often would be as often as you expect to win. There is essentially a baseline range of going to showdown for winning players, but can't say those stats are anything fresh in my head these days ..... got me a lot of review and study (refresh + new) to do if I hope to get back into poker as I would like