trying to pick motors for my bot ... NPC-K2446-6 ?

Hello again helpful friends.
I am considering motors for my robot project. I want it to be somewhat hefty, meaning capable of carrying between 35 - 70 lbs or so of cargo +
robot body weight. The 70 lbs is sort of a maximum, nice-to-have limit. I'd like to have a little more room to play with than 35 lbs as an absolute minimum.
So, after a good bit of searching on the net, I am now considering 2 of the kits from NPC Robotics: NPC-K2446-6 . The description and specs seem to indicate that they more than meet my requirements, though a bit pricey for my budget.
Some questions I have are: 1) How long will these guys last on a given battery ?
2) The only thing about the kit mentioned above that I don't like (besides the price) is the outside bearing block. Although it seems obvious this makes for a more robust wheel linkage, it does add some outside dimension to the bot and make it a little more complicated to fabricate than the basic square with wheels on the outside I was hoping to start with. Any ideas or comments ?
3) Has anyone used the "Electric Drive Train Simulator" software mentioned at Combat Robotics to answer these sorts of questions ( see http://robotcombat.com/store_EDTSim.html ) ? Opinions ?
All comments are welcome. And thanks - JCD
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