We have been following the development closely of drone-runner-kube and it works really well for us.
The only thing I notice is when setting the limits using the environment variables is that it does it per container. This is able to limit well but because each service and step is a new container and they all have the limit it will request alot of resources.
Our example was one build had three steps and with a limit of 2cpus only needed 6 but then when we ran a build which needed 8 containers we then needed 16 cpus which we could not schedule.
I have been looking and I cannot seem to find a way to do limits across the entire pod so have just disabled them for now.