Beta 19 is released with fixed blinking issue.?
Then Sorry to say the problem is is still exist. You can clearly see it by set priority of javaw.exe to low in Task manager.(I am confused beta 19 is slightily slower in perfomance than beta 1, especially in Arial view ?.)
As a value smaller than 1 is not realistic
You are right , but reducing the Refraction Index less than '1' can make easly setup metal like gold.(0.4-0.6) 
My reference sites are : Link 1 , Link2
There's no DPI information in images generated by Sweet Home 3D
I think then the image viewing application or windows read it as default dpi 72.If you are planning to add a dpi value then it must be 300 I wish.
(Human eyes can faked by DPI of 600 
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