Here's a good primer on excess capacity of motorcycles including the Valk:
Valkyrie's excess is about 300 watts.
http://www.powerlet.com/learningCenter/excessCapacityUsing Gerbing heated clothes as an example, you can go to their website and in the description of each type of clothing lists the wattage of each (link below for example is a heated jacket):
http://gerbing.com/Products/Outerwear/eXtreme%20Element%20Jacket.html Kinda just have to figure the math out from there. One thing to remember is that I believe the wattage quoted for heated clothing is at their maximum setting... if you use the controller with them, they will pull less wattage, say at a medium setting.
Also, if I read correctly some of the info I found via Google (can't attest to its accuracy)... a J&M CB is going to max at 4 watts, the Zumo does 7.2 watts. Those are both negligible.
But of course... I am no expert... YMMV