5 * 2560 * 1440 = 18432000 pixels, so at 4-bytes a pixel, that's only ~70MB ? So we shouldn't have a problem just fitting the screens in.
When you say you see issues, what kinds of problems are you seeing specifically?
But no, our virtual graphics device doesn't support more than 8GB of graphics memory at a time. The Guest and Host have some ability to swap things in and out of the GPU, so with multiple applications it should be more of a soft limit than a hard limit.
As far as how much does memory bandwidth help, it's very workload dependent, so it's hard to say generally.
