I've been running them for about maybe 4 months. They are the best investment I've made sense 10 years of racing.
Same with brushless, simply the longest lasting.
I have 2 4800 packs and an assortment of brushless motors.
A side from tires and bodies. The investment is done and permanent as far as batteries and motors are concerned.
If I get 2 years out of my packs like I've heard other people getting, I'm sold.
I'm guessing the pro sponsered guys will stick with sub-c though.