Can someone link me to resources on the efficiency of sticky end ligation?
The best resource for troubleshooting ligations I found (and use frequently) is this NEB page.  That is assuming you've already referred to the instructions provided with the enzyme you're using.   In my case it's T4 Ligase, again from NEB.   It's helpful to check the FAQs and the references listed on that page.    Also, you can make use of their Molar Calculator tool on Ligation setting (see more from first link).

Good luck with high efficiency!