I'm a newish player trying to get better at the game by talking my way through some of its complexities. I welcome informed and experienced opinion, especially, to help me see the map in ways I currently do not.

My vote for most destabilizing CD early in the game is a tie between Russia and France. Each plays a big role in three vital maritime regions (Northern Waters/Baltic/Black and Western Atlantic/Channel/Med, respectively). Russia starts with StP and France has a big say in Tunis, and these territories are often grabs over the major stalemate line to reach 18.

Least stabilizing CD? Maybe Austria, since it is often an early goner anyway, but I feel less strongly about this. England may be the runner-up. Although it is in a nice cozy corner, even in CD England's core territories take a lot of naval resources to nab.

Thoughts or comments?

Austria CD is the MOST destabalizing since austria defending itself is crucial to determing who wins the game.

They're equally destabilizing.

I would say Austria is one of the most destabilizing. Without Austria, Italy can freely move against France with no worries. Turkey doesn't have to worry about the Lepanto. Germany has a lot less help against Russia. The Juggernaut is almost unstoppable.

I would say they are all very destabilizing, but Turkey I would say is the least destabilizing because it will take a couple of years for people to get units and fleets in place to take any of the home SC's. And Russia and Austria would start fighting over them anyways, so things would equal out.

Russia becomes very, very powerful with no Turkey.

Exactly, Russia has no competition for the Black Sea. As said by abge, Italy would be the least destabilising, though strengthening Turkey.

Italy definitely stabilizes the game. The key to stopping EF and RT steamrollers is competent play from Italy.

Loss of Italy is least destabilising.
Most would be France assuming EG make the most of it and work together

The boardgame had suggestions for six and five player games. In the six player game Italy was treated as a CD and in the five player it was Italy and Germany left out.