I did all 4 tests for the CCIP individually. I already had my CCNP so the routing was taken care of. From everyone else I know of who tried, I would go for the BGP and MPLS exams individually. My test taking order was of course routing first, then BGP, MPLS and QOS to end. BGP was the hardest and QoS was the easiest. BGP is a bear, it took me every last secod to finish the test. I finished QOS in halfthe time (45 minutes) and got like a 960.
Obviously your scores will be dependant on how much you study and how familiar you are with the material. I actually only took a class for the MPLS exam, the others I did on my own with self study.
Onto the CCIE routign a and switching now. Really, in my opinion both CCIP and CCNP should be mandatory for the CCIE routing and switching tracks. It's almost a 1 for 1 match on the courseware.