Keep in mind that the rule of thumb is only a starting point. The actual thickness can be different based on individual applications.
Because of their higher strengths, extra and ultra high strength steels can be made much thinner and still retain the same strength levels.
As a rule of thumb it can be said that by doubling the strength one can reduce steel thickness by a third. Or expressed mathematically; Thickness reduction is inversely proportional to the root of the yield strength quotient.
Ideally the higher strength material should be used from the initial design, as in this way the benefits of high strength steel can be maximised. Changing steel grade within an established design often does not fully realise the possible benefits.