That's what I thought to build, both HA and VA and compare performance ( generator can be the the same to cut costs and make whole experiment more data accurate) .
Permission makes me hesitate to build either one of them but the idea is still in back of my head. My garden location is very turbulent place and that's why I consider VAWT more appropriate for this location. Lots of reports say vawt doesn't need tower to be so high as havt so there is less risk it will fall to neighbours' gardens :). When I have some spare time (or money) I think I'll play a bit with stepper as generator and to control load by PWM proportionally to rotor RPM. Just an another idea.
Anyway, your generator looks superb. When are you going to put it up?