[wrxtasy]

What are the key factors to consider for Kodi?
RAM - Is 3 GB better than 2 GB for playing HD Live sports (without buffering)?
SOC - Amlogic 912 better than 905X?

Replacing a Nexus player (1 gb ram/8gb storage) which buffers a lot for HD live sports.

Any other pointers are appreciated too.

We cannot help with situations that involve Live Sports streaming across the internet. There are too many variables in play when that happens. Especially when using WiFi and external, dodgy, Internet File servers using banned Kodi Add-Ons are involved.

I can suggest if using Kodi Jarvis:

a) Try Increase the Video Cache Buffer:
http://kodi.wiki/view/HOW-TO%3AModify_the_video_cache

Also you have fallen into the trap already of looking only at Tech Specs, particularly for cheap Android Hardware. That road leads to disaster.
You need to Read Post #1 of this thread

You would not be asking questions about a S912 Hardware if you had read Post #1.
Any dirt cheap Android device will be not be as easy to use at all as Android TV you have on the Google Nexus Player. The next logical, faster hardware upgrade from the Nexus is the US$69 Xiaomi Mi Box - also running Android TV.