Your biggest gains with the different fuels are mileage... not necessarily power.
Winter Blend gas is something that oil companies refuse to discuss. I believe the truth behind it is that Oil companies do not make as big a profit in the winter due to less driving, and therfore the refineries mix the gas to drop the mileage in vehicles so that they have to buy more gas more often.
If you are going to dyno and tune the car... it may actually be better to do it on Winter gas... because then when summer comes around, your car should have a little extra kick to it based on the summer blend.
Honestly though... it's best to get a dyno & tune with the gas you always use.... otherwise, if something forced you to use an octane lower than what you were tuned for... your car will run like crap.