Cyril,
Did you notice any lag on your system when you upgraded to Mavericks? Did you do a clean install or just downloaded and installed on previous OS? I know you have a formidable system but on mine (which is also not that bad - iMac 3.4 Quad 16 GB) even Safari windows or changing from one account to the next (let alone Sibelius), I am experiencing slight delays. All programs (except Logic 8 which I am not using), is upgraded to its latest version.
Any advice?