I am planning to setup a rig with RX 5XX series. RX 4xx series are more stable for now but I have seen good examples of RX 5xx rigs as well, with regards to hash rate and power consumption after some modding.
I think RX 5xx series will level up with RX4XX in a couple of weeks/months with new drivers and work arounds. Even if they have similar/equal performance with RX 400 at the end, at least they will have better resale value when they are done. Also the prices are almost equal for RX 500 and 400 series for me. Actually 400 series are even a little bit harder to find and some models are more expensive.

What do you guys think? Should I force myself to find 400 series or just start with RX 500?

With respect to pricing;

Sapphire RX 480 Nitro+
>>>
Sapphire RX570 Pulse=Asus RX 570 Strix=Sapphire RX 480 Nitro
>>>
Sapphire RX 580 Pulse=Gigabyte RX 580 Gaming
>>> Asus Rx 470 Strix= XFX RX 470 Black RS

I can buy RX 580 Pulse 10USD cheaper tan RX 570 Pulse.

RX prices are really confused nowadays...