Ok.
Its hard to know what windows will set MTU to if you choose 7k as was the highest possible on my Vista-machine....will it be 7000, or will it be 7x1024?
Who knows
Anyway, my OpenBSD machine only got 100Mb (and doesn't need more, only got 4GB drive in it too) so jumbo-frames doesn't even seem to be supported then. Better put it in its own VLAN or own physical interface, so the jumboframes goes through a router before reaching it. If I manage to set up jumbo-frames between the three windowsmachines that is....