Seperate ranking systems definatly, be cool if they did do this and also had different prestiges to mp aswell, i reckon 1xp for each zombie u kill, and 5xp for dogs and watever else they gonna bring into it, but once you've PaP'ed ya guns u get 2xp.. also round bonus for not dying/going down say 50/100xp.. and everytime u kill 100 zombies without going down u get another xp bonus, also xp for medding team mates, completing challenges, be even good idea to to hav an extra xp drop which gives u double xp for 30seconds.. Treyarch could do soo much stuff with this if they decided to go ahead and doit