Sentinel 30 Degree Doublewide Sleeping Bag

You mentioned hiking with a partner. I cannot cannot recommend enough an ultralight doublewide mat and doublewide sleeping bag combination. There is truly no alternative for my wife and I and we have completed over 100 nights wild camping with this setup. We use a Big Agnes 30F Sentinel sleeping bag attached to a Exped Doublewide air mat. You are effectively packing the weight of one sleeping bag, as the sleeping bag operates similarly to a quilt. But because it straps to the airmat you are completely sealed in, keeping out drafts. It’s definitely pricey, but we invested in it in 2019 and the bag is still going strong. The mat had a free warranty replacement last year and the replacement already has a slow leak that I need to sort. The airmat is split into two sections meaning any slow leak is contained on that side, fortunately. This is the system we use all year round in the UK. We sleep in down trousers and jackets in the winter with green foam mats additional underneath the airmat for added r value. We use a Big Agnes Copper Spur 2p tent.

Since it's currently at full price, the Magma is about $100 more expensive than either of OP's choices. The big difference is that has 800 fill power down, where the other two are 600 and 650 fill power. My daughter recently replaced a synthetic bag she bought while in college with an REI model, and liked their new sizing system. I think she may have bought the REI Magma. I have and like a Big Agnes 650 down bag I've had for years, but at a 15 degrees F rating, it hasn't gotten a lot of use in recent years. I agree with u/TheBimpo that, unless they are trying to put a full set of gear into a pack of 50 liters or less, OP will do fine with either of their choices.