Nick,
Summary: 2x more weight required for Primaloft One versus 800 fill down for the same warmth.
You didn't specify the Mountain Hardwear (MH) jacket model or year of manufacturer. I will make a guess and say it is a MH Compressor pre 2010 model @ 21 oz. This is the most common synthetic MH jacket that I see on backpackers on trips that I have taken.
The older Compressor PL Jacket (OM2734) was produced for the Fall 2008 and Spring 2009 season. These jackets used 114.0 g/m2 of Primaloft 1 insulation. The newest Compressor PL Jacket (OM3163) began production in the Fall 2009 and contains 100.0 g/m2 of Primaloft Eco insulation. There is a significant warmth difference between these model years for the same MH jacket model.
If your jacket is performing at the original specified clo value (highly unlikely) is has an average male thermo-neutral while doing camp chores temperature rating of ~28F and wearing a base ensemble of 1 clo.
Both the amount of down and the type of down are both required to approximate an equivalent synthetic jacket warmth down fill amount. None of the options you specified are close equivalent warmth down jackets designed for UL backpacking. These are a couple of jackets that are: Crux Halo (2011 with long baffles) @ 9.5 oz.; The North Face Catalyst (2010 – 2011) @ 10.9 oz. They are both 1/2 half the weight for the same warmth as a theoretical new MH Compressor using PL1. I used the adjective "theoretical" because tests I conducted on a sampling of PL1 jackets showed they averaged at least 30% less warm than the virgin insulation specs would indicate.
There isn’t a mandatory EN rating for jackets sold in the US for the same reason there isn’t a mandatory EN rating for sleeping bags. The US manufacturers don’t want the added expense of testing nor do they want to compete on value. Since there are many more jackets sold than sleeping bags, there is an aversion multiplier.
There are a few manufactures who lab test and publish temperature ratings for their jackets. They don’t tell you the base layer ensemble clo value or the MET value for the tests because they don’t want you to value compare their jackets to other manufacturers; they only want to show you the spectrum of relative jacket warmth that they provide.
For crude estimations you can use the fact that 800 fill down tests an average of about 1.68 clo per oz. and PL1 is specified .840 clo per oz. As a result you expect about a ½ the weight for the same warmth using 800 fill down versus PL1. My tests show that the ratio is even better than that; when PL1 is quilted into a garment it’s clo per oz. is less than the specified value.
Primaloft is a generic brand name and each Primaloft insulation variant has a different clo per oz. Most variants have less clo per oz. than PL1.