At the current price points ($220 for RX 590, $220 for GTX 1660) there's no reason to consider the RX 590. The RX 580 ($190) is what you should consider.
Windows 7 and 10 both support Freesync, as they have access to the most up to date drivers
thank you for confirmation. I'll think about it. I'm currently on 1060 6gb, and the only reason to switch, after a very long time being nvidia fan, is due to unsupportive freesync under win7. it's a shame really. not everyone wants w10 malware/spyware on their machines.