3 season light weight sleeping quilt

Nate- I think it's going to depend where you're at for determining what rating, for the Rockies I think a 32 F rating is probably average for "summer"

also depends how you sleep- warm, cold, average?

synthetic or down?

if you're looking at 40F you can get into a down sleeping bag or quilt for 16 oz or less

for down bags Western Mountaineering (Highlite, Summerlite, Megalite) and Marmot (Atom 40 and Hydrogen 30) are good ones to look at

for down quilts tough to beat Katabaticgear, the Chiso (40) and Palisade (30) are both worth looking at

it's going to be one of your most expensive pieces of gear, so choose wisely :)

I think it depends on where u plan on doing your hiking as summer/early fall is different in the southeast compared to the rockies.

Enlightened Equipment.

Nate,
If you email a few of the quilt makers directly (this site alone has several)with as much information as you know of at this point, I'm sure they will get back to you with follow up questions and specifics of their respective quilts. I'm sure in short time, they will give you the information you need to make a good decision and get you the quilt you need.

As far as having a 40 degree bag for 3 season use, not only extra clothing, but location, altitude and other considerations need to be made.

It can snow and be well below freezing in July in locations in the US, the High Sierras, Uintas, Whites, … come to mind and much colder in the high elevations of the Canadian Rockies, Alaska, Norway, Siberia,…

If you tend to backpack in the Southern US, 40 degree is fine, even at higher altitudes.