This isn't correct.

A 2100mah LiFe RX pack weighs 106g (from http://media.hyperion.hk/dn/fg3radio/)

The Team Losi 2000mah LiPo pack weighs 86g (http://www.amainhobbies.com/product_...ck-74V-2000mAh).

I couldn't find the weight on a comparable 5 cell NiMH hump pack, but this pack weighs 159g a will provide similar longevity:

http://www.amainhobbies.com/product_...mAh-Losi-Style

One thing you will give up in relation to LiPo is size. The LiFe packs are considerably larger for the same capacity.