If I remember correctly the Power Pack C motors are only rated for 3S. A 4S battery would likely damage them. I have upgraded the motors on my Guinea Pig to handle 4S, but still use (a similar) 30A ESC. I believe the BLHeli ESCs that come with power pack C can handle the 4S voltage, but be sure to double check.
I started out my Guinea Pig on the power pack C setup swinging the 10x4.7 slow fly props. I was running it on a pair of 3S 2200s (one per ESC). With the 4S upgrade I've gone to a 4S 4000mAh battery swinging smaller APC style props. I get plenty of power with this setup and with the differential thrust dialed in it can do some pretty nice vertical stall turns. Not quite honey badger, but still pretty cool for a foamboard cargo plane!
My biggest complaint with the larger slow fly props is that on our grass field the landing gears would occasionally catch on takeoff or landing and dump the plane sideways causing the props to strike the ground. The smaller props don't hit the ground like this.
Read the manuals and documentation on the ESCs and motors in the power pack. It should tell you specifically what they can handle.