This should be a close match, with Ivo serving the way he is, and the fact thst Ivo beat federer last year on the hard courts, so it could get tight.
Karlovic's serve has not been broken all tournament, so i dont know if fed will do it, but if he continues to get 30 aces or more in a match, then you are in trouble.
I think Fed in 4, if it goes 5 then definately Fed. Ivo has never won a 5 setter.
Also Fed said in an interview that he likes playing Ivo, how can you like playing someone who serves like that?