I helped build a -6 (and have 100+ hours in it), and am building a -7 (~ 1 hour in a friend's airplane).
What I've noticed:
Prepunching on the -7 makes some things a lot easier. It doesn't relieve the tedium of deburring edges and holes, dimpling, priming, etc. but fitting and trimming is much easier. The wings were a piece of cake compared to the -6.
The wing attach is much different on the -7; far fewer bolts to worry about. Attaching the tanks makes up for it a bit. Seems in the -7 there are more systems provisions built into the kit than there were in the -6; e.g. by-the-plans fuel system routing is a little different, with pass-throughs in the supports for the closeouts in front of the spar.
The -7 has higher aerobatic (6G) and gross weight limits than the -6. But, the airframe may be a little heavier.
As regards flying them, the two are virtually identical in the air as far as I can tell, with the big difference between the two airplanes I flew being the level of interior fitting-out (doesn't affect flying characteristics, but makes it a little quieter and smoother inside). The -7 seems to have a tiny bit better view over the nose on the ground, floats just a little bit longer on landing, and seems to have power steering with the big rudder (the -6 I fly has the small tail).