You can easily go 5,000 miles on conventional oil today. The performance of today's oils is very nearly what synthetic oil was 20 years ago. Both conventional and synthetic oils have improved, but the gap in performance has narrowed.
You are going 5,000 miles on synthetic and you are worried that you are leaving it in too long? You are changing it more often than needed. I believe in aggressive maintenance so I really don't have a problem with frequent oil changes, but you certainly are not going too far. I'm actually considering going to synthetic oil and performing annual changes. Currently that would be 10,000 to 12,000 miles.