Hi,
Ohter than what rocktalkrock wrote, I have one question, Do you realy have a use for an 8 cores /16 threads CPU?
Or is it a really good price, cause right now you could get a Ryzen 5 1600F (if theres stock on Amazon) for a really stupid price (this is a Ryzen 5 2600 with a tiny frecuency diference), or even a Ryzen 5 2600 which wont stress the VRM that hard.
Anyways, I would go with the Ryzen 7 if its at a really good price and you have a very good power supply, but yeah make sure theres good airflow, and don't try to OC (even if with a BIOS update you can).
If you don't have a great power supply (400w is on the really low side), with this I mean, a very well known brand and model, then I would just pick the R5 CPU which will still be a really good upgrade: R3 2200G (4 cores/4 threads) vs Ryzen 5 1600AF/2600 (6 cores/12 threads).
If you like, share the maker and model of your PSU with us.
Cheers