Selecting the proper graphics card for zmMagik/Event Server

[Farm_Server]

I have 5 cameras at 720p and 30fps(over PoE) now and the system runs fine as is. I would like to add the in the eventserver and zmmagik but am curious what I need in terms of gpu power. I read the github pages for both and it seems opencv needs about 2GB of gpu memory using the Yolo3 config cited in the instructions. Is there a per camera memory requirement as well?

My system is an old AMD rig so I have an 8370e cpu with one pcie2.0x16 slot fed directly to the cpu and another pcie2.0x4 going through the southbridge. 16gb of RAM and am storing about 300 frames per camera in shared memory buffer. I would assume pcie2.0x16 is not going to bottle neck image processing but I do wonder if I can get away with a 4GB card or do I need more memory? Right now I just have a crappy 1GB amd card I keep on standby in case my main pc graphics fail and thats probably barely adequate to run debian.

Space is somewhat a constraint I am using a silverstone horizontal case but there are dozens of options in the 4GB card size, 8GB cards get dicey since theyre all mainly for full size cases on gaming pcs.

Any other things I should take into account? Will the card be running at full power all the time using it for this purpose?