I think it's a simple, equally-weighted, as-needed splitting.

In other words, if both machines need maximum bandwidth at the same time, they are each going to get 50% of max bandwidth. I do not know of a way to set any priority for a connection or a way to limit max bandwidth for an ICS connection.

It should work fine for you though, just as a normal hub/router combo gives up available bandwidth, and that works fine as long as you don't use so much bandwidth that you spend more time in collision timeout than data throughput.

If it becomes a problem, simply spend the money on a LinkSys wireless ethernet switch/router combo, they are getting insanely cheap.