Xref in Tree proxy...or....merge in the proxy?

Is there a preferred method of using vray proxy objects (for many trees for example)?

Should I ‘Xref-in’ the tree proxy from an separate max file? Or, should I Merge the proxy file itself in directly? I am curious if they are the same or is one method better for memory, file loading, render times, etc.?

No need to xref in a proxy - leave the proxy container in your scene. If anything I’d say adding the xref process on top of the proxy process might be slower.