Jordan:
Not to answer for someone else, but I have a sewn thru 40° Revelation (Karo) from Enlightened Equipment.
To address your concerns and thoughts:
To use it down to 30° you will definitely want smaller squares as mentioned above to limit down shift. As long as there is adequate down in each chamber, pushing below 40° a tad should work for "average/warm" sleepers. Adding puffy clothing will take you to 30°, although some will be uncomfortable pushing anything 10° below its specified limit. And of course, when you touch a sewn-thru seam ( and you will) it will, as you say, be uncomfortable.
Oh…one more thought: if your friend sleeps on his/her side you will want an odd number of chambers so they will have a chamber directly above the shoulder when sleeping. Otherwise the shoulder will end up right against the seam, down will shift downward due to gravity and brrrr!
10d Material + high quality down makes for a LIGHT, soft & comfy quilt that packs tiny.
Please post pics of whatever you do – I love these quilt threads!
Todd