I don't think the gunpowder thing is anything against it, since it is a special shoe made directly for him, and as we see, there are consistent quotes of lightning speed, so there's no reason to ignore that.
And the Atomic thing, too, is not good, since it was super casual Atomic and it still climbs above DSK. It's like in Naruto, Kakashi has a Mach 2k feat and Pain has his best feat a Mach 200, but Mach 2k is not for that reason ignored. In fact, this would only make the MHS / MHS + scale of OPM very consistent