Converting to lipo

[Sneeck]

I'm sorta debating to go lipo in a few month's, so naturally I got a question. Would 2 of these pack's be better then 12 gp cell's?

Lipoly 4200mah 2S2P 7.4V Pack

* 4200mah Capacity
* 7.4 Volts
* 35mm X 98mm X 34mm
* Rated at 60 Amp Constant Discharge
* Rated at 80 Amp Burst for 10 seconds
* 245 grams
* Other configuration options available upon request
* Pack comes standard with JST Female taps

(from maxamps.com)

I plan on keeping my 'ol hacker master competition esc with the c50, but if these pack's doesn't give me allot more power over nihm's i'd go for something better. But what?

My main consern is speed and run time, minimal of 15 minute's. Would these pack's work?