A Great Read - "Comparing iRule Control Statements"

One other awesome takeaway was your recommendation to use a stats profile to make sure your if/elses were ordered as efficiently as possible.

Order your if/elseif's with most frequent hits at the top. 
If/elseif's must perform the full comparison for each if and elseif.  If you can move the most frequently hit match to the top, you'll have much less processing overhead.  If you don't know which hits are the highest, think about creating a Statistics profile to dynamically store your hit counts and then modify you iRule accordingly.

For some wacky reason, I hadn't thought of doing that and have basically been guessing at customer behavior. Thanks for that one too!