Slot position is personal. I've bought 1 11/16" preslotted nuts with a range of E-to-E distance, from 34.7mm to 36.8mm.
My last nut is a 3/16" Epiphone nut, and it is 34.9mm. So I think I'm a 35mm guy. The 36.8mm, she was too far for me. Yes, I could get used to it, but maybe I become lazy, and want strings close together.
I would do two things. 1] Order another couple blanks. 2] Visit your favorite guitar shop with a small accurate ruler. Find a few guitars with the same neck width, play them, and decide which spacing you like best.
Having hundredths, 128ths, and mms all on the same ruler, you can probably find one unit of measure which gives you an exact E-to-E measurement which is easily dividable by five.
Keep in mind, I'm a completely untrained amateur, so like my ex-wife, who learned to add and divide some arse backwards way her grandmother taught her, most anything I do is from a self-taught perspective.
