Interesting...
The figures given (above) for Jet B would give it a lower SG (around .804 against the .840 given for A1) so I'd be surprised if the calorific value where higher (not checked).
Following Gem's thought though, it may be that the lighter of the two fuels would be burned at a faster rate if fuel burn relies on Lbs. per hour (but that rating would have been given for only one specific fuel).
If its calorific value is higher it may result in eng. overtemp.
Is the hypothetical engine rated for both fuels? Is it a hypothetical engine?