Although related with XBMC this tip is intended to Raspberry Pi community (it’s also possible to all other XBMC clients).
I’ve experimented several skins aiming a better user experience and performance, from all Refocus was the best. Refocus is able to give a very good user experience and the best performance for Rasbperry Pi. On System -> System Information my RPi was doing (at best) 62fps @ 1080p (which is awesome!).
Download this file and copy it to Download network share. Enable repository from Add-on -> Install from zip file -> Home folder -> Download . Then go to Add-on -> Download add-ons -> Jeroen Repository -> Skin and install it.
Give it a try and post your feedback!