If you're going to tank beyond regular 5-man instances, you need to transition away from a spell-damage set into a defense/avoidance set. Right now, you are probably doing a great job of generating threat, your DPSers love you, and you burn through mobs fast. It is probably rather difficult for your healer (if he's at the same level of gear and experience as you) to keep you alive through fights, particularly longer ones. Switching to the "recommended" gear will indeed drop your threat generation (but if you already have the CFS, it won't drop it too far!) but your gains to survivability will allow you to succeed in more advanced content. Your DPS can always dial down their damage, but healers can't necessarily surge their heals to keep you alive through crazy boss spike-damage.
Experience has shown that for prot pallies, the optimal balance of spell damage and defense will come from specializing +spell damage on your weapon and maybe shield, and from +defense (and +parry, +dodge, +block rating) on your armor.
Losie's Pre-Heroic Tanking Sticky is a great read for practical info on this topic, but I also strongly recommend ThelsDeKwant's Defense and Mitigation sticky if you can handle a deeper but more abstract explanation of how you will gear yourself.