Fuel econ - Carby 4.1 vs MPEFI OHC 4.0

[The MaDDeSTMaN]

Ok, as some of you know, I've got my stock standard (for now) carbied 4.1 XF, and LuvinmyEB has a JMM enhanced (just Dev 1) EB GLi. They're both auto, mine being 3 speed, hers being 4 speed.

Last time her car was run on a dyno, it put out 118rwkw according to the dyno at JMM, and that was BEFORE the extractors were bolted on. I personally have my doubts about that dyno figure, but even 110rwkw would be respectable and well within possible if we assumed a roughly 10% dyno error, which I'm sure it wouldn't be out by that far. Given that it pulled that sort of power, there wouldn't seem to be anything wrong with the engine I'd guess - massive blowby, tuning problems etc would lower the dyno figure, right?

Anyway.

I would have thought the EBs EFI 4.0 would get better fuel econ then the carbied 4.1, particularly with decent extractors, a decent exhaust and a pretty much new high flow cat, but with both cars driven in the same manner, the XF gets an easy 100 to 150kms more to the same amount of fuel. Given that there doesn't seem to be anything wrong with the engine, would it simply be because of the shorter diff ratio (3.23:1 vs my 2.77:1), or could it be something else, like a dying/dead oxy sensor? I doubt it's the 4 speed in the EB too, if anything that holds higher gears longer then mine does and is more reluctant to kick down a gear, even with full throttle.

It's odd, I always thought EFI would be more fuel efficient, particularly with a decent exhaust setup, but that doesn't appear to be the case.