While we’re nitpicking, I might as well point out that both of you are wrong.
Original Exige rims are 8.1kg / 10.2kg = Total 36.6kg
seven-split-spoke rims are 5.8kg / 7.8kg = Total 27.2kg
Difference: 9.4kg
Edit:
If you are to believe the data on the SELOC Wiki, it’s actually even more at 12.2kg (8.8kg/9.8kg vs 5.5kg/7kg). I’m with the first one though.
Cheers Phil