Yes, my fear is that the 850 would stall before reaching a good speed, it has more load resistance (turning the rotor) and it electrically loaded up at a slower RPM than the 450.
If anything, my own greed reversed with the testing, as now I see the 850 needing large props and gearing to get that extra wattage, and the 450 being much more suited to produce in moderate wind with small prop and no gearing. It's MUCH easier to get to that magic 240RPM with the smaller motor. In fact, if that prop has a LOT of speed, and little torque, the 750 may work better in the moderate winds, so that's why I threw that one in the box too.
After looking at the power outputs, it was obvious that the 850 wouldn't be putting out twice the 450 until very high prop speeds with double the load. And double the load may exceed what the prop can push, so in reality the 850 may be sitting idle in the breeze while the 450 trickles some watts into the battery.
My thinking - is that the 450 will make more USEABLE power than the 850, on the size of prop you already have, simply because it will not stall as quick and will spin up faster. The 850 will OUTRUN the 450 in gale-force winds with a heavy load, but that's not exactly a 'light weight' turbine is it? You won't get any more power out of the 850 without larger blades, and probably gearing to match the same rotational speed as the 450 on a smaller faster prop.
Anyone that has DONE this can chime in any time and let me know if this sounds correct. I'm not leading SF down the wrong path am I?
Remember I have YET to fly a turbine, so I am spouting only what I have learned from reading.
Now if I am wrong, and the props you have spin it out of control (yes those babies do really CRANK), then we can look at the 850 again later. But the hope is that the 450 will put a tricle-charge into your shed batteries whenever you have a good breeze, since these usually come with clouds that put the damper on the solar cell. And in a gale, you can approach 100W, and maybe a good 50W on a moderately windy day (front passage).
You will need a 3/4" (19.05mm) arbor to fit the blade hub to the 19mm shaft of the 450 motor. I found 5/8 and 1/2" arbors at Windy Nation, haven't found a 3/4" arbor yet.