If i had to guess i'd say the rears are about 20%. I know they aren't as light as 35, and 5% is wayyyy darker. 20% is what i'd guess. Sometimes those light meters aren't very accurate which might be why we had a few different numbers above. I had a cop one time tell me my 5% was like 25%, so it just goes to show if those meters aren't configured right, or if the test is done incorrectly.
I've got 5% on top of the factory rear tint. It makes it like 0%. It's pretty awesome. Although a bit dangerous when backing up at night time.