I use a Beseler MCRX and have both a condenser and a VC-CLS light source. The VC-CLS head is the only one of several variable contrast heads which I tried which has a surface larger than the cross section of a 4x5 negative.
WIth either of these heads, and a 150 Rodagon lens, the upper bellows completely collapsed, I have never seen any sign of vignetting, even if I choose toprint with the lens wide open. When I used a 135 Componon, although there was no hard edge, there was significant light fall off in the corners.
I don't know how this will help you, but it is my experience.
Jim