You are way ahead of where I arrived when trying to build VAWT's, but I want to pass on an important lesson I did learn:  When changing the rotor diameter, you think you are gaining in torque, but you are also changing the "solidity" of the rotor, and its preferred tip speed.  The operating RPM could drop drastically, compared to the proportional increase in diameter, robbing your alternator of the RPM to produce enough EMF.

Ed has witnessed a phenomenon called "powering up", which is actually what happens if your rotor exits the stall zone, and the wind speed provides more power to the rotor than the generator can remove.  On a HAWT, this is commonly dealt with by furling, but there's no such system on a VAWT.  You don't want to be around if that happens.  Ed's rotor is designed to run at low enough RPM, even in high wind, that it doesn't get into trouble.  If yours runs in a faster speed range, watch out.

Now re-read what I just wrote:
paragraph one - don't reduce the speed, you can lose power instead of gain.
paragraph two - don't increase the speed, it can blow up.

I was boxed in.  That is why I abandoned my VAWT project.