Off the top of my head, I think that the front axle in everything except the Rubicon is a Dana 30. I don't think that there is any difference between 2 door and 4 door with regards to axles.
Also note that the front Dana 44 on the JK's is not a 44 in the true sense. It's apparently somewhat smaller and less beefy than the Dana 44 rears. Seems to work okay though - especially for the folks that have gone to Chromoly shafts and added gussets.
Personally, I'd probably lean towards buying a Rubi is I thought that I would want lockers. Yes, ARB lockers are sexy...but you'll end up spending more money to build an X up to a Rubicon standard.
The exception to this would be if you're planning to upgrade beyond a Dana 44...say going with a Dana 60 if you want to run 37's or something larger. At that point, I'd think that a base "X" model would be the logical starting point.
As to whether or not that Dana 30 will handle 35's, I don't have any first-hand experience. The consensus seems to be "Maybe". I guess it probably depends on how much you like the skinny pedal. If you're dead set against buying a Rubicon, then MOPAR will sell you a 44 front as an accessory.
Keep in mind that all of the above is just my opinion, and I'm new to Jeeps. I like my 2008...but I'm not speaking with the kind of background experience that some of the members here have.