I would advise reading this section of the GKE docs. It explains the marginal gains in allocatable memory and cpu from running larger nodes https://cloud.google.com/kubernetes-engine/docs/concepts/clu...

For memory resources, GKE reserves the following:

255 MiB of memory for machines with less than 1 GB of memory 25% of the first 4GB of memory 20% of the next 4GB of memory (up to 8GB) 10% of the next 8GB of memory (up to 16GB) 6% of the next 112GB of memory (up to 128GB) 2% of any memory above 128GB

For CPU resources, GKE reserves the following:

6% of the first core 1% of the next core (up to 2 cores) 0.5% of the next 2 cores (up to 4 cores) 0.25% of any cores above 4 cores