This -
http://www.toolstation.com/shop/Pow...8V+Li-Ion+Cordless+Fuel+Impact+Wrench+/p29162
Is listed as having a max torque of 950Nm.
If my sums are correct, that's the same as getting a spanner, 1 meter long, and hanging a 15 stone chap off the end of it.
Pity its close on £500. Seems like it would be quite useful!