As I said the discussion is based on at all cost maintaining the current FL by cross feeding to deareate and then how to deal with the resultant imbalance. This is known as conformity bias where you look for data that conforms your decision rather than for information that would contradict it. Nobody is willing to take the option of descending to FL300 and stop the cross feed. If any one cares to look in the manual he will find that the difference in LRC FF at ISA+10 for a GW of 60 Tons between 370 and 300 is 8kg/HR/Eng. Just use gravity feed on failed side at FL 300.