I put 444s and monotubes on my bike ('12 FLHTK) back in November, and can only say that it is a different bike altogether.
I specifically went with HD springs since I ride with the wife quite a bit, and when solo I like the extra firmness. That extra stiffness is not for all, to be sure, but it works well for me.
"First it's pretty tires, then it's pretty guns...next thing you know, you're shaving your beard and wearing capri pants."
- Si Robertson
'12 FLHTK Ultra Limited, Vivid Black, Stage II (Rush True Duals and Slip Ons, SE-204 cams, SE/K&N AC, PCV, SE Push Rods & Lifters), Progressive Monotubes and 444s