Convert your query to use placeholders (ie pass in ? for each parameter, and then in the execute pass in the data) and performance should improve greatly. More importantly if load matters, hard parses use a type of internal lock known as a latch, and latch contention will cause Oracle to scale very poorly.

Of course prepare_cached with placeholders will perform even better, but just switching to placeholders will make Oracle perform much better.

To understand Oracle's performance characteristics, I can highly recommend virtually anything by Tom Kyte. He has strong opinions on how to use Oracle (some of which I disagree with) but does a very good job of explaining how things work and giving you the tools to explore further.

UPDATE: As noticed by jplindstrom and etcshadow, I misread the code and the hard parses issue that I talked about is indeed a red herring. However if you are benchmarking, be aware that if the real code does not use placeholders, then hard parses will be a problem for the database, and you really want to avoid them.