Peter,
Perhaps we should talk in term of how stiff and powerful the rod is along with how far down the blank it bends with a mid-length cast. This would give much more information about a rod than the very subjective terms slow/medium/fast.
Anyone who knows me or has hung out here for a while knows that I like rather stiff, powerful rods that bend furthur down the blank as casting load increases for casts with more than 70 ft of a long-belly GS or XLT, whether a heavy line rod or a light line rod. A very good friend and excellent spey caster doesn't like rods as stiff or powerful as I, he prefers a medium-stiff rod that has reserve power in its butt. He likes to feel the rod bend furthur down the blank without having to really put to muscle to it to bend the butt. Another very close friend prefers a rod with a little stiffness but with enough butt power to be able to make 90 ft casts with a mid-belly line.
Notice that none of the three of us like or use a noodle; but that each of us has very different preferences in rod stiffness, power, and rod bend under load.
For example, the T&T's, GLX's and Loop Greens that I like are pretty stiff, powerful rods that require quite a bit of power to be applied to bend to the cork under casting. The CND Thompson Specialist is a moderately stiff rod with a somewhat stiff and powerful butt that bends to the mid-point of a bit furthur under all but the most powerful casts. The Meiser FES is a bit less than medium stiff rod with a medium power in the butt that flexes about 3/4 of the way down the blank under even moderate casts. However, the FES has enough reserve power in its butt to power out long casts without collapsing when enough power is applied to bend it into the cork when casting.
Which one of these actions is best? simple, the one you like best. Which one of best for casting long-belly lines? again, the one with the power and stiffness you like best. I like stiff and powerful rods, so? They simply allow me to put a lot of power into a cast, which I do because my prefered spey casting style uses both arms, shoulders, wrists, and hands to power the cast. A combination of a rapid underhand pull with the lower hand and top hand push, and the stiff rods allow me to do this without overloading the rod or creating tip-bounce.