The Top 2 are actually pretty simular. It is the same Company (CNH) and both share the same engine (to correct you, both have 692hp). I really love the Quadtrac but now that there is a new T9 I like this even more.

Probably the reason why Big Bud Don't figured in this list is because of is technologies and fuel efficiency my guess...but its the biggest and more powerful tractor ever built in my opinion :

For next time: Horsepower is not so important, it`s torque that gives a meaningful idea of actual power in machines like these

I would look into Northern Montana at the Big Bud 747. That's the biggest tractor in the world. Recently it was reshoed and it is still working fields in this state.

Id like to see some of these with a pull match with the old stem locos used for ploughing. And I know which would win..it wouldn't be these....Check out the Case pulling a 44 bottom plough....make these look toys...

You missed Versatile tractor model 610DT 650HP. then there is the Big Bud 747 which is the most powerful tractor ever made.