I haven't shredded mine on 6 cells yet but on 7 cells I stripped 2 diffs in less than 5 charges. Course I've only been able to run 2 charges on 6 cells sofar with all the rain we've been getting. And even with 16/84 gearing, my speed meter showed 30 mph top speed so it's much better than stock and will wheelie on 6 even with the added weight of an aluminum brace and RX pack in the front.
You will probaly want to look at the MGM 80 as it has an internal BEC and is cheaper than the 9918. I am going with the MGM 80 and the Lehner 4200 combo for my rusty.
I'm pretty sure the 70 amp rating is the continuous rating for the warrior or Mike wouldn't be so fast to recommend it with the 8S. I haven't had any problems with it. Also it does have a BEC but that's only good for 8-10 cells, any more or less and you need an RX pack. However, I'm inclined to agree with Mike that with a Stampede, this is one time adding more weight in the front is a good thing.