hopefully i'm not jumping all over someone elses thread but I think we are after sort of the same thing..
I can consistently put out 250w riding singletrack trails on my MTB, sometimes 350w on a short climb. i'm after assistance that can let me ride a bigger bike (more travel, stickier tyres) faster (so my flat trails become more like a gravity bike park) for more loops, but at the same intensity i currently ride at - personally i think that if someone can make a light, quiet, discrete and torque responsive unit that will retro fit to existing mtb's they will shift huge amounts, even at quite a high price.
I appreciate the trail access issues that plague the USA and probably drive most of the anti e-mtb sentiment, but basically nearly every mtber i know would happily go for an upgrade that gave them bionic legs, which is what this is about, just the noise/system weight/stigma that is currently preventing it - 2 of 3 appear to be right at the technology threshold of vanishing and the 3rd i think will just go away once enough people try the systems.
Digging a bit more and playing with the calc sheet that miles provided, it does seem that 250-500w would provide the extra assistance I need but the more important factor for trail riding (rather than just a lift to the top of the hill) is going to be a spot on torque sensing system, so i'm probably stuck waiting for something like the e-ram or brose to release a standalone unit.
glw plans to the original poster!