Latency will not be much effected by number of clients.

12G system ram will not run 20 clients.

Must mean he has two 2G video cards.

There is no possible way you will run tiled with each tile in full resolution. You will really be hurting for screen space if you tile all 20 on one monitor.

You can run full screen like I do but flipping though 20 screens isnt practical.

Anything over 10 clients and you need more then one computer to be practical.