REI Igneo 25 or Igneo 17 seeping bag

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Looking for advice on the REI Igneo 25 vs 17. Seems many say the temp ratings are a bit optimistic. I'm afraid the 17 will be too much for my needs and feel the 25 would probably be sufficient as I section and generally go out in temperate weather, but if the ratings are really that far off maybe the 17 is the way to go.

For reference this will replace my old Columbia Reactor 35 bag rated at 51/43/21 Fahrenheit for Comfort/Limit/Extreme. Recently back from a Deep Gap NC to Fontana section where at night it was probably around 40 give or take, first few nights I was cold but went to bed in clothes the rest of the trip and was ok. I'd imagine the Igneo 25 rated for 35/25 Comfort/Limit plus clothes would be fine, but if it's really that far off should I go for the 17?

[Time Zone]

I've read reviews - I think on REI's website - claiming that the Igneo 17 has far less insulation on the underside, meaning it may not be suitable for side sleepers if the bag rolls with you (and it's a slim-fit bag, so it may well). To me, a bag that has little insulation on the underside might be inferior to a quilt in some ways. I'm not a back sleeper, so as poofy and discounted as the 17 is right now, it just looks like the wrong tool for me.

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Hmm maybe I should have posted this into the General Gear Talk forum. Mods could this be moved?

[Feral Bill]

They have zippers. Warmer is better. You can easily adjust to shed excess heat.