I would do 9/16. This will give a little more than 75% threads.
75% threads are for bolts and stuff, and made for high-speed tapping.
I just ran some with the 37/64 drill, and I got a full or very nearly full thread form. If it's not complete, it's within .005" on the diameter of complete. I'm looking at a flat on the top of the thread of about .006" and I would guess it's probably what? .004" at 100% thread?
This is with my eye, but I can't have more than .010" flat on the ID thread, and it looks a lot closer to .005"
It threaded to my Tornado threaded bolt gun nice and snug.
I was using a split point titanium coated HSS bit. American made. The import s--t probably cuts .005-.010" oversize, something to look out for.
You know what actually, I know the reason why- the chart is calling out 5/8-18 threads. The 5/8-24 thread is a finer thread, IE larger hole size, so the 75% drill for a 18 pitch is more like a 85-95% drill for a 24 pitch I believe.
It took me a while to remember. It's been a while since I bought the bit.