In central MD & Northern VA, and sleeping in a poly T-shirt & running shorts on a 1" Thermarest under a tarp with the wind-ward edge on the ground, or in a tent with full net inner (both have about the same amount of breeze & lack of heat trapping).
In early spring & late fall, I'm comfy in a 15 deg Marmot 650 fill down bag.
In late spring & early fall, I'm more comfy in a 32 deg down bag. (In the 15 deg bag I get hot, open the zip, get cold area, zip up, get hot, zip open, etc all night).
In summer, I'm comfy using a 300 wt polartech blanket. (200 was too cold at 2am).
In winter, I use the 15 deg bag, add a foam pad to the thermarest, and sleep in a Tshirt, 100 wt fleece shirt & long johns. I swap a 200 wt fleece jacket for the shirt if it's colder than usual.
ps: The 650 fill 15 deg down bag + Tshirt & shorts is about the same warm as my 20 deg Sierra Designs 3D Synthetic bag + Tshirt, 100 wt fleece shirt & sweat pants.