Update: i got a response from Nvidia techsupport:
If you were to monitor free -h you would see file system cache filling up memory. Between clips you can run sudo sync && echo 3 | sudo tee /proc/sys/vm/drop_caches > /dev/null from a shell window to empty the file system cache. You will get back all the performance.
So i did this and yes it helped. Here are some of the temperature results and time to render 5s video clips, after using the suggested cache clearing above: the available memory didnt change much so i dont understand the significance of that. Temperature hit 86 deg.
here are the screenshots:
