How much is Iceland/Norway/Western Europe warmed up by the Meriodional Overturning Circulation? A shutdown in the circulation was associated with the Younger Dryas stadial, also referred to as the Big Freeze, so I'm curious how much warmer Western Europe is due to the MOC, and how much heat (in Joules) the MOC actually releases into the region.
To answer the numerical aspect of your question: Rintoul &amp; Wunsch 1991 advanced a poleward heat flux in the North Atlantic (i.e. that generated by the Gulf Stream) of $1.3\pm0.2\times 10^{15}W$. 

That number of 1.3 PW (PetaWatts) have been reused in several reviews on the thermohaline circulation such as Clark et al. 2002; hinting that this number is at least realistic (since I'm not a physical oceanographer myself it is difficult for me to judge otherwise). 

References:
Clark, P. U., Pisias, N. G., Stoecker, T. F., Weaver, A. J. 2002. The role of the thermohaline circulation in abrupt climate change. Nature, 415: 863-869.
Rintoul, S. R., Wunsch, C. 1991.Mass, heat, oxygen and nutrient fluxes and budgets in the North Atlantic Ocean. Deep Sea Research Part A, 38: S355–S377.