There are two widely used methods for computing octane, the one with the lower numbers is used in the USA, so yes, 87 octane in the USA is what the manual says to use.
Being far from a professional driver, I use either what the manual says, or the lowest octane the engine will not knock going up a hill on. Hence 89 octane in the Cadillac, even though the manual says 87 (and "slight engine knock when driving uphill is acceptable"--not in my car!).
Jaguar states the use of lower octane fuels is acceptable if the timing is slowed, so I imagine the same would be true for Mercedes. Now, who would but a performance car then slow the timing....