Here is the deal I learned about 7 cells...it is common sense when you think about it.

Peak a 6 cell shotty and you get sometimes aroung 8.5 or so volts depending on your pack. You might get low punch with maybe 5-10 amps of burst but 8.5 to 9 volts.

Look at a 2 cell lipo...fully charged and ballanced you are looking at again, 8.4 or so volts, a hell of alot more punch (15c-45c punch) which is a HUUUGE advantage not to mention more consistent continuous voltage, predictable dropoff, very low discharge rate (when it is sitting overnight) not to mention a serious weight savings.

7 cells (unless in open class) COMPENSATE for the punch of a 2 cell lipo with VOLTAGE! Unfairly when i peak my crappy Venom 5000 bash packs they peak at 13-14.5 VOLTS!

2C lipo to 6 cell is more fair but the lipo has the clear advantage. Take out a 7 cell and although you'll be driving a tank you will be pumping almost double the voltage of the lipo which can't be overcharged like a NIMH.

The punch may feel similar but it is because of the gobs of voltage it needs to be in the same game.

Save the 7 cell for the open class or something.