Yes it's confusing.

I don't know where this 8MHz version was dumped from, I received the rom dump anonymously(maybe you know who ). Though I don't think it was dumped from a SteveUK Amsterdam T8 4MHz repro PCB.

About real T8:
T6 is around 5 to 6MHz, on an overclocked R65C02P4.
T6 was around 1000DM. T8 was around 1200DM. If T8 has a weaker CPU and the same chess engine, the price increase can not be explained.