RCgroups "scirocco" says:

if you focus on weight and Kv, you will get into the ballpark and it will also allow you to compare motors regardless of labelling and vendor.

Building on Doug's comments above, weight straight away is a pretty valid indicator of power handling, again independent of inflated vendor claims. You can exploit weight in a number of ways. First off, if you know your power requirement, it tells you you should be looking at motors of at least a certain weight. Or if you have a tail heavy model you may choose to use a bigger motor than strictly necessary for power handling, noting that electric motors are a lot lighter than their glow cousins, where it counts the most right up front. Or if you've got a specialised requirement such as a 30 sec motor run in a glider, you might be willing to push a small motor hard, accepting lower efficiency for weight savings.

Max current rating is important, but don't be afraid to discount it if it is giving you unrealistically high power levels based on motor weight.

Then Kv. First off, don't think of Kv as a rating, which implies a figure of merit. It is a characteristic, a bit like colour. Red is not more colour than green, just different. Similarly low or high Kv is not better or worse, it's just a characteristic you choose to suit your application.

Kv HAS to be considered together with voltage and IMO is NOT analagous to high and low gear ratios for that reason.

Looking at your statement "a lower KV rating could be used with a higher diameter/pitch prop to produce more torque / climbing power,". More accurately, at the same voltage, a lower Kv motor of the same size as a higher Kv motor will use a larger diameter prop to at lower rpm to achieve the same power. While it is true that at the same current the lower Kv motor will have higher torque (torque is proportional to the inverse of Kv x current), both the low Kv and high Kv motor at the same current will have the same power (torque x rpm), remembering this is a same voltage comparison. If you only need to fly slowly, the slower turning big prop will be a better solution as the larger diameter prop will be a bit more efficient, but the tradeoff is top speed will be limited.

If we take out the common voltage, then your statement is no longer valid. For motors of the same size, 6S and Kv=400 and 4S and Kv=600 will run the same size props and require about the same power - just at higher current for the 4S.

Ron is very generous to quote an older post - there is an expanded discussion on motor selection methodology in my blog that might help some.

Keep the good questions coming

Now it is necessary to determine the blade angle versus the radius, the helical path each portion of the blade follows as it passes through the air. Without consideration of the AOA, the tangent of the helical path at any radius is obtained by dividing the design forward speed by the rotational velocity at that radius. For a plane with a design speed of 200 mph, we multiply by 22/15 to get the speed in feet/second. To get the rotational velocity at a given radius, we multiply the radius, in inches, by 2 x π x rpm/60 x radius/12. With the engine operated at its rated 2800 rpm, we would obtain 63.4 degrees at 6-inch radius, 36.9 degrees at 15-inch, and 21.8 degrees at 30-inch.