Do you have access to an air compressor? If so, get all that dust out of it.
It’s amazing how much that dust increases fan speeds and temps in the 4,1 and 5,1.
When I first obtained my 5,1 it came from a house with cats. Was full of dust and fur. I was shocked how much dust came out of it. I saw temp drops of 10-15degC after clearing it all out.
FWIW I grabbed a Sapphire RX 580 Pulse 8GB from Amazon UK for $182 delivered to Australia.
Not as good as the deal of a free 5770 listed above though