0-30 is the same viscosity at operating temp as 5-30 or 10-30. It is only thinner than 5-30 and 10-30 when cold, but even then it's cold viscosity is higher than it's hot viscosity. When comparing oil viscosity ignore the xW-xx viscosity ratings and look at the measured viscosity. It is usually listed in centiStokes, abbreviated cSt.
If you look at the Mobil 1 product pages you will see that the 100°C viscosity for M1 0W-30 is 10.9cSt, while the 5W-30 is 11.0cSt and the 10W-30 is 10.1cSt. In other words, the 0W-30 and 5W-30 are virtually identical while the 10W-30 is actually thinner at operating temps! Cold viscosity (40°C) for 0W-30, 5W-30, and 10W-30 is 62.9cSt, 61.7cSt, and 63.2cSt respectively. In other words, their viscosity are all basically the same at 40°C and in all cases are nearly 6 times thicker than at operating temps. What the charts don't show is the cold flow pour point which is where 0W-30 really shines. If you live somewhere that gets really cold (i.e. below 0°F) then 0W-30 will reduce startup wear. For those in warm weather climates there is no real advantage or disadvantage. It certainly won't increase wear.
As for the oil consumption, you won't necessarily have more blowby if it's the rings. The compression rings can be in good shape while the oil control rings can be varnished and no longer keeping oil out of the cylinders. As another pointed out, valve guide seals are also a possible culprit. Not sure about the valve guide seals on the Atlas engines though. Does it puff blue smoke on take-off? Chrysler engines in mini-vans, K-cars and the like are known for valve guide seals going bad, which is why you often see them puffing blue smoke when they take off from a light. You could also be sucking oil through the PCV valve. Again, I don't know if that's a problem on the Atlas engines...
