IME 6-8 mg of 5-MeO-MIPT makes for truly outstanding erotic enhancement. You might notice a little ejaculatory inhibition at first (definitely not to the degree of MDMA, however) but with a little persistence you'll be rewarded with a soul-shaking orgasm. :D
Also, at least from what I've observed, women seem to get along better with tryptamines than phenethylamines, so for your benefit and your girlfriends, I'd go with the 5-MeO-MIPT. If you're determined to get a decent amount of sleep, though, you're gonna need to take it in the late afternoon/early evening. Hope that was helpful