Help creating a low budget Hyper 7 brushless

[DrKnow65]

Have a quick request from guys who run 1/8th brushless buggies....

I've settled on a 6S/1580/MMM setup, question I have is wieght VS runtime, i.e. I'm looking at either 2x3S5000 in series at ~2lbs -or- 2x6S4000 parallel at 2.8lbs
Basically it's 5ah at 2lbs, or 8ah at 2.8... is the extra .8lbs worth a 40% increase in capacity. Total wieght (just a quick calc w/o all the parts assembled yet) 5ah= 10.4lbs, 8ah= 11.2lbs