GPU Minimum Requirements

There are a number of efforts underway to develop a GPU miner.

Is there any indication, at this point, what the minimum GPU card requirements are likely to be? For example, with Ethereum, you have to have at least 2GB of VRAM (soon to be 3GB).

My current ATI cards are HD7850, HE 7950, and a RX7 370 while the Nvidia cards are a GTX 550TI, GTX 480’s and 460’s.

I run Linux Mint 17.3 (built on Ubuntu 14.04) and LM Sarah (built on Ubuntu 16.04) on multi-core Phenoms.

Thanks for any help you can provide.