I am trying to export the highest quality possible ( for showcase ) not for game, but even with 4k textures and max iray export somehow the face textures looked baked and low resolution i want to be able to see skin textures just as you can see when you are on skin gen mode so why does it lower the quality anyone knows? and can you share the maximum quality so you can get face textures look like realistic 

Open the Preferences panel - Ctrl+P - and make sure that "Max Texture Size" is set to at least 4096 x 4096. Also make sure that you also use the same texture setting in the "Iray Render Globals" section of the Preferences panel.

You should also read this thread for some tips on getting the skin colour to render correctly.

Gerry

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System: Win 10 Pro (21H2), Asus X99-E WS, CPU i7-5930K -3,5 GHz, 32 GB DDR4 2666-16 RAM, NVidia GTX 1080 Ti GPU - 11 GB VRAM(Driver Studio-536.99), Samsung 850 Pro 512 GB SSD, 6 TB HD storage.

thanks so much! did that but still skin textures looked baked and super low poly ! it seems almost like using normal render other than iray has better results? i want to make ultra realistic renders but so hard to achieve that anyone knows how?