I think Solong's 1 in 10 to 1 in 6 is about right.
Out of around 9 contacts, you can pull around 3 dates, and have sex with 1.
Where efficiency goes up, is often in contacts to dates or dates to sex. This is from a guy with high skill, better than average looks, or very well off with cash.
Like having 9 contacts and getting 6 dates. Or have sex with 2 women out of every 3 per different dates he goes on. So sex with 1 out of 6 per contacts collected from women is excellent.
To get below 1 out 6, from what I've seen, requires something very unusual. Like a guy who's a 9, rummaging through chics that are 4s or 5s. Which is weird. Usually such a guy would want chics at or closer to his level. And when he goes up against other 8 and 9 score females, his batting average will usually come down. Like hitting in the minor leagues versus the major league.
Even if he was content to rummage through 4s, he may run into issues, because the women may think he is scamming them or they have extreme insecurities about their looks. And even lower level chicks, if they think the guy is desperate, can play hard to get. Just out of spite and feeling the power of having the perceived advantage.
A fat or ugly chick can be at times as equally difficult than getting a really hot chick in bed.
Another level of efficiency for guys is maintaining a team/group of women. That is, instead of 1 night stands, he keeps the women (if she doesn't run out on him), and keeps ADDING. Some guys don't realize, that's how you get 3 or more in rotation.
By the way, WOMEN, do this too. They are just way sneaker about this or can afford to drop guys faster. Getting guys for sex is easy for women, so many don't keep a team of guys, which can be DIFFICULT to manage. If they are horny, the WOMEN do the 1 night stand (these days), then drop the guy so there is no evidence. Thus women love and have fun with online dating and night clubs, way more than men do.