Personally I don't think Naruto will ever become Hokage, but I do believe Luffy will become the Pirate King. Theoretically, if both goals were to be achieved, I'd say Naruto's would be at the end of his series whereas Luffy's may happen towards the end and continue on.

There's not many similarities between the two anyway - they both have a dream and both dreams are very Shonen-ish, that's about it.