Client Source address

Have you configure advanced logging to capture the header?

http://blogs.iis.net/deanc/iis7-8-logging-the-real-client-ip-in-the-iis-hit-logs

Also, you don't need x-forwarded-for enabled in both an iRule and your http profile. Chose one or the other. The profile would be more efficient. Also, if at all possible I would recomend moving to IIS 8.5 on 2012R2 as it now has Enhanced Logging which is easy to add any header or cookie value to your logs from the IIS logging management console.