I am on my way out the door so I will keep this short. They don't state how much down is in the jacket, but the Plasma most likely has 1.6 ounces of what they quote as 1000 power fill down.
Our position is that 1000 fill down doesn't really exist in practicality.
In order to get a 1000 fill rating the down is measured in zero percent humidity, and the down has to be fluffed with warm air.
The instant it comes in contact with something humid... like your skin it loses loft and loses its 1000 power fill rating.
The Plasma uses a 7x7 fabric(7 denier with 7 ripstop), weighs 5.2 ounces and cost $269.
The Montbell Extremely Light Down Jacket uses 1.8 ounces of 900 fill down, uses a 7x10 fabric(7 denier with 10 ripstop), weighs 5.6 ounces, and costs $189.
In ProLiteGear.com's opinion, the Montbell Plasma is a marketing piece, the Extremely Light Down Jacket is a better option.