Thank You !!! You are right, Fps drop in GTA V is mainly caused by single channel memory.I tried Battlefield 1 & Farcry 5. In both games it performed closer to other RX580s.....
Wattage !!! It took me more than 2 months to figure out the voodoo behind this. Most of the stock RX580s draw 110-130w during gaming by default.It's the overclocked one that draws 180-190w. Unforunately in many videos I have watched there were only few displayed the power draw. Today I found a clip that showing Stock vs OC perfomance.It explained the mystery to me.
4GB vs 8GB ? , Yeah considering same manufacture and series (Gigabyte Aorus in my case) there specs are same.1365Mhz clock , 2304 stream processors.I am new to 1080P Resolution. For many years 720P was my native resolution so 4 Gig was more than enough for 720p. In that time CPU was the bottleneck of my system.I am looking forward to upgrade this to R5 3600.
Again Thank you All !!! Now I can sleep well after all the sleepless night I wasted on this.