For people coming from AWS, we currently don't have an instance shape that lines up with the c3/c4 ratio (pushing you either to our n1-standards or n1-highcpu-. Can you get by with less memory?
Note: we're very aware of this pain point, and maybe you'll see something soon ;).
We need maybe 1GB for each job, but we need some leeway to avoid the OOM killer when a group of work units is larger. Swapping takes so long that it's not cost effective.
But to be honest about the situation, the cost would have to be much lower to make it worthwhile for me to rewrite our scheduler on Google's API.
Note: we're very aware of this pain point, and maybe you'll see something soon ;).