RE: Beneifits/detriments of additional winds on AXI
This is a very good question and one that I have been thinking about for months now.
For non-outrunners like the high Kv geared brushless motors (Aveox, Kontronic, MaxCim, Hacker) the effect of turns over Kv is more obvious. Additionally, you have another variable to play with in the gearbox reduction ratio. Adding more cells adds more power quickly.
On the lower Kv outrunners like AXI motors, I have not seen a benefit to using the higher turn versions as the increase in cell count provides little power increase when you factor in the extra weight of the cells.
Looking at the specs for both the [link=http://www.hobby-lobby.com/brushless_axi.htm]4120 and 4130[/link] motors, the power output to the prop is very similar, only the weight of the motor, cell count, and the RPMs are really different.
Basically, the larger, heavier motor allows you swing a bigger prop at the cost of even further efficiency reduction which is compensated for by adding cells (and therefore weight). The real measure of how well your plane will be powered is by counting the watts to the prop which is more commonly seen as watts/lb.
The 4130 has slightly more power than the 4120 and also allows you to swing a larger prop. Ideally, it would shine more if you could use Lithium cells. Lithium cells provide less weight and higher voltage for a greater power density.
When using NiCd or NiMH cells, the additional cell count from the 4130 may negate the power benefit. For example, 16-cells on the 4120 produces 900 watts and 30-cells on the 3oz heavier 4130 produces 980 watts. The weight of 14 extra sub-C cells plus the 3oz from the motor is about 1 pound! The net result is 80w extra for an additional pound...virtually nothing.
My current feeling is that the best benefit comes from using the lower wind version of each size AXI motor. The motor design itself brings additional benefits of simplicity (no gearbox) and maintenance-free operation (no screws to loosen or gears to oil).