If you find that the YARPP database calls are still too database-intensive, try the following:
turning off "cross relate posts and pages";
turning on "show only previous posts";
not considering tags and/or categories in the Relatedness formula;
not excluding any tags and/or categories in The Pool.
All of these can improve database performance.
Where are these settings??
I don't have anything like this under Settings / Related Posts (YARPP)