Can we please not do all this "my bike is too stiff" nonsense again please?
Think about it for a moment.
Right, how much suspension travel do you need to make your FS bike more comfortable than your HT?
Thought about that?
(Hint, it's rather more than the 0.1mm - 0.8mm of flex you get even in a very very flexy HT frame)
Now conduct a quick experiment on elasticity:
1) take both wheels off your bike, lift the frame above your head, and drop it onto the floor. How high did it bounce?
2) repeat with one of your wheel/tyre. How high did that bounce?
Hopefully by now, you are starting to realise that the "Stiffness" of a frame (and in fact its frequency transmission bandwidth) is so many orders of magnitude higher than the perturbation frequency/amplitude from road inputs that it is irrelevant.