Setup Advice

I am wanting to build an E-Maxx to keep up with a couple of stock T-Maxx 3.3s. I can't sped a lot of money on LiPos so I'll be running 12-14 cell IB4200s. I already have a MM ESC from another project and plan on running that with a 7 or 8xl. I'm not worried about flat out speed runs, just bashing in the back yard and maybe some racing on a basic track.

I know there are a lot of variables, but what kind of runtimes can I expect using 4200s and enough gear to keep up with the Nitros? If I'm going to be stuck with 15 minutes of run then cooling cycle and re-charge before running again, I'm wondering if electric is going to be the best way for me to go.

I thought about trying a 14S2P NiMh pack but thought that might get a little heavy.

AWESOME FORUM by the way

Thanks in advance
Jay