Same basic airframe for all three. On the 6 & 7 you can switch from tail wheel to Nose gear in a matter of hours. The later models have a boot cowl and engine mount had been extended further for weight & balance using 912 series engines. My 5 is limited to 100 lbs in baggage area (without forward sweep on wings) where later models can go 150 ibs. Later models have a shorter wing tip and trailing edge of tail has been squared off. I'm sure there are more minor differences.