I believe lots of people have found it will cope with 5V but of course that's out of spec. They're only a couple of dollars if you burn one out though. I guess

I believe lots of people have found it will cope with 5V but of course that's out of spec. They're only a couple of dollars if you burn one out though. I guess it comes down to how much hassle it will be for you if you need to replace the ESP8266.