Hmmm, I don't know anything about the Dyna family, never having owned one. I am familiar with the Softtail Std. I have an "06" with 45,000 miles of riding on it.
At low speeds it is not a fun bike, it does not balance all that well. Sharp curves are not the fxst's forte. Long sweepers it is ok, my "sporty" was great on the sweepers, lay it down and roll the power on. The softy must be "horsed" around and never feels real solid compared to the sporty. Straight down the highway is fine.
I am convinced the "skinny tire" up front lends itself to the handling problem. The "fatty" in the back has a much larger foot print versus the front which can make for some interesting cornering from time to time depending upon conditions.
I NEVER ride in the rain unless I have been caught out in the open. NOT SAFE on a fxst imho.
Two up riding is fine and the "boss" and I have enjoyed riding all over Texas, Arkansas and lower Missouri. Good luck