I have nano (pre a spec) 6600 65c's and one reedy 6500 65c competition pack.
Love the nano's for the price, the reedy has a little more punch off the bottom end and holds power a minute or two longer before I notice the power dropping off. Both have about the same run time, but the voltage doesn't sag as soon as I'm nearing LVC on the reedy.
Granted, that's about 9 minutes into a practice run (11 min to LVC), in a 7 minute heat, can't feel either start to sag... just messing around on a practice day.
Is the reedy's performance worth more than twice the cost of the nano? Guess that's different for everyone. In a race, having that additional pop when I nail the throttle is nice. It's not a huge difference, but it is a difference.