I would defiantly load the OS.,,and COD aswell., I just have a 90gig ssd, and have COD, DCS BS, and A-10, and FB46(4.10) all loaded on it. 20gigs left.,,with no performance decrease, definate improvement with ssd's.
Edit.,if you don't already know., never defragment your ssd. not a wise thing to do apparently.