I want some excess pump capacity to allow variable speed engine operation. 

Using oil from the sump with the existing hydraulics.  So far in about ten hours running it did not seem to be outrunning the existing cooling provisions.  I'm not really adding capacity to do more work beyond what the existing system is capable of, except for brief periods of time.  As the guru who has been helping me with it says:  We can run it just great until we get to the headland, then it all goes to ...... in a hurry."  I need to have the separate functions (and I suppose the extra capacity) for those 45 seconds or so every five to ten minutes.