I agree with 2/3 of the above post, the part about fractal not needing to make one, and the part about finding the best thing that suits your budget. Technically if the reference is full range flat response, they should all sound similar, if they can achieve flat response, but the differences will be coloration at certain frequencies and off course how well the speaker reacts to the amount of power that it gets.
But I know from owning several different pairs of FRFR's that are very close to FRFR technically, they are and should sound similar It's not like taking a 4 x12 Marshall cab versus a 4 x12 Mesa cab, which are going to sound wildly different... They should technically sound much closer than that.