"1.2 clo would provide about 75 F lower sleeping comfort limit if you were naked inside."
Ah Jerry, now you've done it - you've gone ahead and introduced scientific values that help destroy marketing hype. ;|
To the OP, you might consider searching some of R Nisely's older clo value threads. In essence, you need a clo value of around 3.25 to be comfortable sleeping at 55 degrees F, and, as Jerry notes, around 1.2 to hit 75.
Interestingly, you only need a clo of around .8 (ie dressed) to be comfortable **sitting** @ 70-75. That means you're burning approx 1.5x as many calories sitting vs sleeping.
For those considering Sierra summer bags, 30 is the usual target range since it can (and does) dip below freezing even in August @ higher elevations. 30 requires a clo of around 6.5, which loosely translates to around 7.5 oz of syn or 2.2" of down loft. (Hence the 2" of loft [one side] in the 32 degree WM summerlite.)