Lots of good information to work with there to try to give you some suggestions MD, except the most important thing... what your intended use for the new barrel will be.
Personally, I'd opt for the 17 Rem on the Contender, and go with a 19"-20" barrel. Will balance better and be easier to use off hand in the field, yet with the right forend would still be excellent for bench, bags or bipod. You wouldn't suffer any appreciable loss at all over a longer length - actually will shoot a little more precise with the shorter tube.
Forend length/width also depends on the use - I'd go no more than 12" and light to medium profile for offhand, longer and beefier if for shooting off bags/bipod.
FWIW, I own several Bullberry carbine barrels and all but one are 20". They work very well either offhand or off bags/bipod depending on what forend I have installed. The short folding calling rig (6X47) wears an 18" light sporter profile.
HTH
Ladobe