First of all, x is clearly better than 3D by the north hand. It is more descriptive, allows you to take preference to 2S with a bad hand, and every once in awhile, allows you to pass with a heart stack. To answer the question, 3D is nonforcing, but shows extras. I think pass is logical with the S hand, but 4D is possible. I like pass more; I'm willing to compete to 4D over 3H. I don't think 4D here should be forcing, just plain-old invitational to game.