u/Immediate_Drawing301

Hoping folks can help me understand the comparison between two bags. Because either something funky is going on between the two manufacturers stats, or I don't understand down insulation and compressibility.

I would have thought that with 900 fill vs 650 fill, and with 3oz less down, that the Feathered Friends would pack down smaller than the Mountain Hardwear Bishops Pass. I'm wondering if other people can tell me whether there's something I'm missing?

Given the 900 fill down is it harder to compress into as small a size? Or not recommended to preserve the loft? Or alternatively is Mountain Hardwear sucks all air out and compresses it under lead weights (i.e. extreme conditions and not real world) to get to the 8L packed size?

Feathered Friends Petrel 10F Medium vs Mountain Hardwear Bishops Pass 15:

900+ Fill Power Ultrasonic Muscovy Down vs 650-Fill Down

Fill weight: 1 lb 5 oz / 595 g vs 1 lb 8.7 oz / 700 g

Average weight: 2 lb 1.3 oz / 974 g vs 2 lb 8.2 oz / 1141 g

Packed size: 11L vs  8.3L

A long time ago a guide told me that if you add a liner to your sleeping bag, it's the equivalent roughly of adding 10 degrees (Fahrenheit) temperature rating to your bag. Wonder if anyone has tried this out in conditions where you really needed the extra 10 degrees and it worked for you? Debating between a 20 degree and a 10 degree sleeping bag, and wondering if this trick might help me extend the season of a 20 degree bag.

Hey folks. Considering upgrading my sleeping bag and investing in a Feathered Friends bag. Female, debating between the Egret 20 degree and the Petrel 10 degree. The 20 degree bag is likely the perfect one for the JMT. The reason I'm considering the 10 degree bag is so I can have it for extending my backpacking season in general, i.e. not just for the JMT.

Reason I'm posting here though, is I'm concerned about being too warm on the JMT in late July, particularly at the lower elevations (going SOBO). I know you can always unzip a too-warm bag, but just wondering if folks have any relevant experience/perspective to offer, especially if you're directly familiar with FF bags? I'm going to get feedback on the two bags from FF directly and in other forums, but would be especially interested in direct JMT experience. thanks!