After being a member here and paying attention to the discussions on engine performance, I would have to conclude a few things to better your life span.
1. A proper air/fuel ratio, and usually running a little richer than the factory settings.
2. Use quality oils as always suggested.
3. Use HD sugested fuel octain ratings.
I guess the rest is, where and how you ride. I would like to hit at least 60K before opening up the top end or case, a 100k would be great.