My son's pc was upgraded with an RX570 vga card. As integrated graphics is not needed any more, I want to use the 3400G in an other configuration. I'm considering to replace it with a 1600 AF (3600 is out of the budget). How would it effect 1080p gaming performance? I'm a little concerned about the lower clock speeds of the 1600 AF.
Depends on the tasks you're using it for... in most games the higher clock speeds and newer architecture of the 3400G will pull ahead of the 1600 by 5-10%. Though with a bit of OCing and tweaking you'll get similar performance in games(maybe better for the titles that require more cores).
On the productivity side the 1600 will be much better hands down... no contest there.
Considering the incredibly low price of the 1600 AF it's totally worth it.. as I said for 1080p gaming you won't feel the difference between them.