PCIe x16 bifurcation to x4x4x4x4 then mixing Gen2 and Gen3 cards - will all be Gen2 speed?

Does anyone know if the bifurcation specification requires that all the bifurcated channels must have independent timing? That is, if I bifurcate a x16 Gen 3.0 slot into x4x4x4x4 and then plug three Gen3 and one Gen2 cards, will all four cards operate at Gen2 speeds?

Thanks!

 

asked Supermicro; they said they do not know - have never tested such a setup - but in general they think one card should NOT affect the speed of another even if they are plugged in the same slot (using bifurcation and passive slot splitters)

 

Should not affect anything because the negotiation of the speed is done at the RC, root complex and each device is connected to a dedicated foot complex. This is purely from a system engineering point of view.

 

I'd think not, but this is one I'd like to hear what you find.