Ciao Mikko,
mine is from 2013, and made with Carbon D-box. The steel is 12mm.
I have installed a Leomotion L4023-2400 and a 6S 35C Akku with 2600 mAh (ca 400g).
In addition, a RX Akku LiIon 2600 fairly in the center.
Presently I fly it without gear for weight reason, the plane has already 6300-6400g, without gear and without anything extra inside.
I do not understand where the overweight relative to the Producers info comes from, he claims from 4,9kg.
The Motor and Akku mostly replace the lead which would be otherwise required. I guess the difference to a glider version is considerably smaller than 300g.
best regards Andre
PS: the plane flies very well and dynamic, possibly because of the weight.
But anyway, published data should not be so far from reality....