Kram is correct that d20 > 12.3 for DD efficiency, but that does not mean it is best use of energy. That depends on where you currently sit at DD. My guess, not knowing the specifics of your current fusion progress/status, is that extra energy should go to 12.3 brutal. Especially once you are done with dragon, then you are no longer double dipping. In brutal 12.3 you will be triple dipping...
Most efficiently doing an individual event creates fusion inefficiency. Always think big picture.
Psst - regarding D20: stats