KFW 50EE or 40EE - Is the upgrade worthwhile?

I just don't see any advantage in timber frame... whether I have a solid construction built in 10 months or wait 12 months for the production of a wooden house is basically the same in the end

Exactly. Where there is no difference, there can be no disadvantage either. I am (with the "normal" - i.e. Energy Saving Ordinance or KfW55 - house) also not "pro 'prefabricated' house," but on the other hand also against the fundamental rejection, because the onsite-built solid masonry house is equally equivalent. However, it applies

and probably almost the same price

only under the condition of the "normal" standard. With KfW40, the step from the standard there is usually noticeably smaller with the timber frame panel builders than with the masons. Otherwise, it is indeed true that "with the same equipment there is no fundamental price difference."