Did I upgrade or no?

Also, the EMS bag is in great shape. Only used 3 times and been stored in cotton bag most it’s life.

A 750 fill bag (all other things,shape,size fabric cover,baffles,  being equal ) can have 10% less fill to give you the same ratings but that is about it.

Checking the specs of the S2S Reactor liner, one version is fleece and weighs about 14oz and the “thermolite” one weighs about 9oz.

Either way that’s a fairly large weight and bulk penalty that would better be invested in a bag or quilt appropriate for the anticipated low temperature without an additional liner — extra down weighs a lot less than any liner.

However, there is absolutely nothing wrong with using your down parka (and also down pants) to supplement your sleep system. Just make sure the sleep pad (air mat and/or CCF) is also ‘up to the task’ because the warmest sleeping bag or quilt will disappoint if heat loss through the bottom is not held to an absolute minimum.

The only accurate way to compare the warmth between sleeping bags is to measure the overall loft of the bags while they are laying on the floor. If two bags have the same inches of loft, then they have the same level of insulation even if their fill power is different. Of course there are other factors like the cut of the bag (mummy vs rectangular) or features that prevent heat loss near the zippers and neck, but generally measuring loft is an accurate way to compare. If your new sleeping bag has the same inches of loft and is lighter, then yes its an upgrade.

I bet that if you have two sleeping bags cut the same and with the same amount of the same down but one bag has a (moderately) heavier fabric the result will be less loft but the same performance.

well I got the EMS bag in the mail and it loft just as mush as my sawtooth when both on the floor next to each other. The sawtooth in noticeably heavier and bulkier when compressed.  I’ve never been cold in the sawtooth and been certainly been out in it in sub 20 degree weather.  I feel the EMS bag will serve just as well but will be lighter and smaller. Like I said earlier, if I know I’m going to be out in the super cold i’ll already have a 800 fill lightweight down jacket that I can sleep in also. All in all I think the sawtooth would keep me warmer but I also think that bag is under rated in terms of its EN rating b/c they bag gets hot. But I don’t think the EMS will have any problems keeping up here in the south east where I do most my hiking now.  Miss Colorado everyday:(