Hi!

I'm planning Machu Picchu & Annapurna gear list. For both I'm being recommended a -10C sleep system, so I would like to invest once to cover both these treks.
I currently have a Marmot Phase 30, so far from fitting the temperature. I see 2 options :
- I buy a sleeping bag/quilt that covers -10 : simple solution, but it limits the use of it to these 2 treks only (or at least this type of treks).
- I buy a quilt to use with my Phase 30 (current idea being EE Revelation 20 as outer layer) : the versatility of the layering system would theoretically cover all types of trek I could do in the future, however I'm reading on different forums very opposite opinions - some love the layering system, some state that the compression of the outer layer on the inner results in loss of insulation and therefore doesn't work/too risky.
I'm not an expert, specially for these mountain treks. Do you have experience in using a layering system for those, or met with people using it? Any recommendation?

Thanks!