well my system is nearing 7 years old ... intel core 2 duo at 2.4 ghz . my only new item so far is an ocz vertex 4 ssd. My frame rates have not dropped in raiding. So I doubt it is your cpu now causing you issues. I have no suggestions tho ...save mentioning over-heating possibly throttling your gpu. But even it that were true.. it would not go down to 5%. So ya, I will stick with the cpu is prolly fine
But what are your graphics set to? The thing with WoW is performance varies wildly system to system, and being a CPU intensive game, I can only imagine upgrading my CPU will help performance. Some systems should blaze WoW no problem yet they have low FPS for no reason, while other seemingly low spec systems run the game just fine. It seems to be a common issue where older Intel setups still run the game fine where brand new Intel and AMD setups have the same issues that I am experiencing. I have guild mates who run similar Intel chips to you and they didnt experience any FPS drop with the expansion or patches, but they arent running on ultra settings.
Like I said, before the expansion on Ultra settings I was getting 30+ fps in raids, with drops to 20-25 when things got really heated, but now I get 15 fps max once we engage the boss or a group of enemies.
I will install the new CPU tonight and see how it goes. I will report back to help others in a similar situation.
Also heat is not an issue, my CPU load temps are never above 30 Celsius and my GPU never tops 60 Celsius.