That makes it a but harder to reason with i think - the chip may well be a complete re-map of the fuel injection type stuff which might throw more fuel in to get more HP, but again i could be very wrong about that.
If you can get more HP and run a larger prop i am convinced fuel consumption will be less, but this might be more about torque than HP, in which case i think you would need a bigger boar (more cc's) to swing another 2" of prop...
..in short i dunno.
I'd get the 115 if the price is reasonable and weight the same.
I'd have a 175 opti on mine if it was not about £3k more