There are no such thing as a 4x5 lens. Large Format lenses are just that, lenses that are mounted on a box with a bellows to simplify it a bit.
They have different focal length and speed but most important they also have different image circle and it is the image circle that is important. A 150mm lens can have anywhere from 140 to 400mm IC depending on the design of the lens.
The point Jesper is making is important if you go with a 6x17 back for your 4X5 it is also important to think about shorter focal lenght lenses as you may not be able to compress your bellows enough to focus at infinity.
A dedicated 6x17 with the propper cone for your lens of choice will be nicer to work with. The disadvantage is that you almost need to dedicate that lens to the 6x17 as mounting, calibrating and removing again takes time.
That last sentence worried me, so if i choose a lens to attach then it will be a pain in ..s to take it out to use another lens?