[Exim] Reccommended retry times / queue run intervals

I have an SMTP mailer server handling only remote SMTP, currently approxiately 10000 - 150000 remote SMTP messages a day. What sort of retry times shoudl I be setting to keep the queue to a minimum? Also, I have been running sperate queue runners every hour or so. Is this worth doing, or would it be better (from a ssystem load point of view) just to set shorter retry times?

Thanks in advance

David Rigby

drigby@???