I see you already booked, but just to add. I've done both and I enjoyed the KttK tour a little more. The backstage was good, but it could have been better. First issue was when we were back stage at American Adventure. Our tour guide referred to Susan B. Anthony as Betsy Ross. Betsy Ross died when Susan B. Anthony was 16. Two totally different women - both great figures in American History. We all corrected her very quickly. Second was you were on the bus, off the bus, on the bus, off the bus. Third for the money you paid it really didn't feel special or VIP. That's really my own issue. Fourth it would have been cool to have a mechanic or service guy come talk to us about Tower of Terror and the what his/her typical day is. It was cool to see the "ride cars" up close, but it lacked. And lastly our tour guide was just not that into it. There was no excitement or enthusiasm from her.
Side note: Walt Disney: Marceline to Magic Kingdom Tour is another great tour and at only $35 it's a steal. I did this for my 39th bday and we got to see the HM Ballroom scene from under the track. It was awesome. It was funny we were not allowed to cross a white line because we would show up as ghost on the ride. They said a maintenance worker stepped over that line and freaked the guests riding above out.