Want to get the most performance out of your Raspberry Pi XBMC system?
First of all, I recommend using RaspBMC, it has built in overclocking and a custom version of the default skin built in.
I have recommended in the past using this card (Amazon Affiliate Link): Transcend 8 GB Class 10 SDHC Flash Memory Card (TS8GSDHC10E) it really is the fastest to date SD card and around $10 it is the number one performance upgrade you can make to your Raspberry Pi.
RaspBMC has a built in safe overclocking system.
To get there go to Programs>Raspbmc Settings>System Configuration>System Performance Profile.
You will see the following options: Normal, Fast, Super (in order of increasing performance). I used to keep this at “Super” but have been having some problems recently, so I have changed mine to the “Fast” setting. I haven’t noticed any real performance issues and it seems much more stable.
Your Raspberry Pi is capable of outputting to 1080p, but most content is only available 720p or lower so this will speed up the functionality of your system without much of a noticeable difference in playback. If you really are watching mostly 1080p Blu-ray content then feel free to leave this on 1080p, but 720 (1280x720p) really is the faster setting.
To get to this setting go to System>Settings>System>Video Output>Resolution 1280x720p
This setting really helps when navigating through folders with a lot of video files in them. The system will no longer process each file and take thumbnails to display. If you use a media scraper or another method of storing thumbnails, then you won’t want the system to extract thumbnails anyway.
To get there: System>Settings>Video>File Lists>Extract thumbnails and video information
RaspBMC comes with its own modified version of the default skin, Confluence. Keep things light and fast by leaving this skin selected. Also, try to limit add-ons to the bare minimum, this will help speed things up especially boot up times.