As I am sure you are already aware the 5800x is a bit faster than the 3950x. This should tip the scales in the R7 favor for most games.
It would likely be worthwhile to read up concerning your rendering program to see if it benefits from core count or speed outright. The additional cores would seem to me to make a possible difference there. If you search YouTube (for instance) there well may already be a review on the specific rendering program you utilize for this task.
It may also be worthwhile to consider the RAM cost/speed as a part of your decision, as well as cost of motherboard robust enough to deal with the CPU you choose.