Sorry to say this PAFred, but this doesn't answer the question at all!
The question was what amount of load step can be performed AS A PERCENTAGE of the full load rating.
This is depending on several items, such as engine BMEP, whether the engine is turbo charged, moment of inertia, governor performance, generator AVR design, etc.
All of this is quite clear explained in the manual on the website as already mentioned by me on the 9th December 2002.
Differences in Engine versus Generator power rating is not always caused by bad intensions of the supplier, but is mainly done for one of the following reasons:
1) The same engine and generator power rating is not available a standard batch line product. In this case it's common use to size the generator bigger as the maximum engine power. This in order to prevent overloading of the generator.
2) Project requirements for overcapacity of the generator in order to reduce the temperature rise of the generator, (for example if the the maximum ambient temperature is high)