Great 'Old school' Rock tone there Tom, :D
I can hear where the Mules will potentially cover more sonic ground than the Riff Raffs alone ; with the tone sounding fatter / heavier in the mids and warmer in general. On the bridge pickup, there is still that cut and 'sing' though. The problem being ( as with all the B.K.P. I have heard and owned ) - that an S.G. with either 'flavour' of pickup in it will sound good and so that the choice can gets ever harder, the more B.K.P you try.
Perhaps you can fit a 550k volume control in the bridge circuit, to open up the contrast even wider ? I fitted some B.K.P 550k pots in my Jazzer - and the difference was very clear , from 500k. An even cheaper ( and infinately adjustable ) mod than the bridge / tailpiece. Even if you do get a set of Riff Raffs later on, you will still have what I feel to be the most adaptable B.K.P. ( Mules ) in the armoury. :)
