I3 8350k can be clocked at 5ghz so would be better for gaming, the 8400 is locked so I'd recommend 8600k if going i5, either get the i3 and save for the i7 8700k or save now and get the unlocked i5
I'm probably going with the 8350k it's just so much value for the price. It's amazing how much performance they are getting out of the chip, compared to last generation