Here's an inside pict of my Parallel Dual Cell. It's not faster than normal. Just has more torque (I bypassed the resistors going to the motor) and longer runtime.
As you can see the only difference between a regular Zip and a Bit is the size and even that's not much.
I haven't gotten a Zip SE yet and doubt I will. People on TinyRC have both good and bad things to say about them though.