Mind muscle connection is key as we already know, and to really achieve that you cant just workout fast, but super slow isn't needed either.
I remember in one of Ronnies DVD he talks about how the muscle don't know if you used free weights or a machine etc. as long as you train right the goals are achieved (given your diet and supps are in check too).
So if slow reps, fast reps etc works for you, do it, or mix it up a bit.