"I know that natively has historically been the best performing, but it seems like that is changing with FB heavily investing in react native."
"Do you see any downsides of using react native anymore?"One downside is it doesn't support Android so its not really a total solution for mobile. Another downside is React Native is very early stage and the documentation isn't great. Lastly, you are relying on Facebook instead of the platform maker so React Native may lag behind each new SDK release or be canceled at any time. For example, they have another framework for doing very similar things to ReactNative.
In general what I've found is React Native has a lot of value for bringing web engineers onboard to develop mobile software. However, it provides little value for exiting native engineers. So its definitely worth trying.
One last thing. I'm not convinced you can build an amazing app with 100% react native, probably much less depending on your exact application's needs.