GoldenTaco, the Shindengen really is the best option at this time for the 650GS, it is still a shunt regulator but faster acting and with less internal power consumption and hence less heat than a stock VR because of the FET components
The compufire sounds good but we are pushing it beyond it's stated maximums. All the reports are good though and so for the F800 in particular where stator temperatures are in serious need of lowering it is the best choice. There is another unit mentioned in the thread out of Roumania which is higher in max ratings but no one has used it as yet
In terms of reducing engine load, while we have permanent magnet alternators the ability to do so is relatively limited with the serial VR being about it other than fitting a lower output stator.
On the cars they have brush type and you can reduce voltage to the excitor coil easily and in addition to that some have a clutch arrangement which is used to disconnect the alternator under various conditions like acceleration. You will see over at bimmerforum and elsewhere people retrofitting firmware to do at least some of this. BMW's figures on fuel saving and increased engine output are a little surprising