Which SS montbell

I can probably figure this out on my own and it probably is not such a big deal since the difference is 5dF but thought I would ask anyway.

For about 2 weeks I have been unable to decide if to buy a Montbell SS UL down #4 bag (35dF and 1#7)or a #3 (30dF 1#9) long bag.

Difference is about $50.

I already have a summer synthetic quilt and a -20/-30dF or so down bag, so this would be more of a high altitude summer, spring/fall or used in combo with the quilt as a liner.

Thanks