(but really though, Apple retail and corporate systems run a version or two behind because they need the stability. so his iPad probably still is on iOS 6 until the bugs are worked out of 7, just like his Mac is still on Lion or ML)
Considering his age, and lifestyle, I think he probably has the iPad Mini top model. Since he hardly has time, he rarely gets to tinkle with it as much as MR users, and thus it does run smooth, just as it does for the other regular users.
Cook's iPad has 10,000GB of Ram and a whole lot of special stuff that not only makes it smooth as silk, it is lighter, thinner, has perfect color registration, and does Searches for him before he even asks.
I hate to say this...but even the maintenance staff at Apple has a better iPad than you!
I think someone like Tim, or any CEO would just use stable devices like standard consumers. Placing advanced tech in a design could cause problems maybe?
Besides, Apple make great products. So yeah, I'm pretty much sure they'll use the same devices as consumers.
He and his iPad/Mac are rarely (if ever) customer facing. The fact that we have to speculate over what he uses is proof of that. They have so many specialized apps for important Apple systems that security and stability are more important than how it "looks."