For $170, you can get a 12oz 900FP, 10d kit from TH that will come in around 18oz (12 down, 6 fabric). Here's a review of the P30 from Backcountry:
Other summer weight bags are better!
By: gear freak
October 10, 2011
Although the Plasma 30 is very comfortable and fashioned from some of the best ingredients available, we believe that other bags perform better in the ultralight summer category. For one, the Plasma has a full neck baffle with two snaps and a drawcord. While this feature is well designed we don’t believe it belongs on an ultralight summer bag. Similarly, the hood is very comfortable, but almost too comfortable. Marmot stuffed extra down into the back of the hood to make a mini pillow. These features don’t add too much extra weight, but they illustrate that the bag is designed more for comfort than for performance.
Baffle design: continuous horizontal baffles found in the Feathered Friends Merlin and Western Mountaineering Summerlite provide more versatility than the Plasma's vertical baffles. The Flow Gates (7-8 in each baffle) are made of no see um mesh neeting and cover most of the baffle. You can pass some down though them, but it's quite difficult. Continuous baffles are better because you can shift the down to the top of the bag if it's very cold and to the bottom if it's warmer.
Another potential drawback is the shell material, Pertex Quantum. Though superlight and surprisingly durable for its weight the material offers virtually no water resistance. Other materials, such as the Pertex Endurance UL offered on the Feathered Friends Merlin, are nearly as light and more water resistant. You can’t go wrong with the Plasma 30, other bags perform better and are cheaper.