You can put a 2700mah NiMH pack in the 3PKS if you want, you can put a 3300mah 3S lipo in it if you want, but why would you want to, are you going 2 weeks racing without the ability to charge it?

I'm putting a 3S ProTek 1700mah lipo in my 3PKS for 2 reasons, first one being lipos are lighter and have no self discharge (well they do but its very little comapred to nicad/nimh) and the second reason being that after a while of using the stock 700mah nicad its starting to lose its capacity as nicads do, so its time for a replacement.

As for getting me through the day, 700mah does it no problem at all.