Hi Ruairihev,
First, you can change the grid voltage of the Power-One Aurora inverter in case it gets too high (and disconnects) during backfeeding of the grid. The AuroraInstaller program will let you do this, as well as the inverter's front panel. We often raise them by 5 Volt on installation, since the grid here is very 'weak' in many places (high impedance, so the voltage shoots up during backfeeding). The inverter has a window around the grid voltage as set in the inverter, for North America it's from 90% ... 108% of the set value, for your region that could be slightly different depending on regulatory requirements.
For wiring, when I plug in the numbers for 920 feet (280m), 6kW, and 240V phase-to-phase, I get 3.8% losses with 6 AWG copper wire. For aluminum wiring (cheaper) you would need 4 AWG for 3.8% losses. In general, we shoot for 4% losses or less at peak power. Keep in mind that actual losses overall are much lower than this, since wind turbines do not often run at peak power, most of the time they run at a lower output. Using 3 AWG copper would give you 1.9% losses, which is nice, but overkill IMO.
I would avoid adding a transformer to the mix: They cost money (6kVA is not cheap), and add losses. In particular you will have stand-by losses even when there is no wind.
Rectifying 240V 3-phase at the tower base will give you about 325V DC, and 18.5A. If my rather quick math is correct, you'll get 4.1% losses with 6 AWG copper, and 3.3% with 5 AWG. Of course, in this case you need just two conductors instead of three.
Running wiring at 230V AC single-phase is going to be worse, it's 26A, and losses go with the square of the current. In that case you would need 3 AWG for 4.1% losses, and 2 AWG copper for 3.2%.
From the above, I'd recommend moving power through 3-phase wild-AC from the turbine. 6 AWG copper wiring is not bad (and not too expensive). You'll have to do the conversion to square-mm.
By the way, I see a large number of Aurora wind inverters that get destroyed by overvoltage. Please make absolutely sure you have something in place so the DC voltage into the inverter never exceeds 600V (or about 440V AC 3-phase). Relying on a dump load is often not enough, I've seen many turbines with dump loads blow inverters. A voltage sensing relay and contactor to positively disconnect the inverter at a set voltage is better.
-RoB-
