I added the comment in FT that VRAM is not doubled. Performance increase depends. iClone is not a game, so reported increases for games may or may not apply. 

This article provides some insight: https://www.pcauthority.com.au/Feature/441170,the-sli-question-is-multi-gpu-worth-it.aspx. 

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Since it was one of the first questions everyone asked, I thought I would make an issue of it in the feedback tracker. We would like to have multiple GPU support going forward.

Here is the feedback tracker link.