There are a lot of people who compare Starkiller to Luke in that Luke is a weak force wielder and not very powerful. The main issue with that logic is that ever since Galen Marek was a child, he has been vigorously trained by Vader for 10+ years to be a sith lord. Luke barely started training with the force before episode V. I think Luke has the potential to be really powerful for 2 reasons. 1- he is the son of Anakin (big bonus points) and 2-he was able to take on Vader after hardly any training at all............but he got his arm cut off, so I guess not a flawless victory.
anyway. I think that line "not with you, no" was a big easter egg of somekind. like Vader knew his son existed. Remember, he knew padme was pregnant before she died, I don't think he would have forgotten that and maybe through the force he could sense the future and search his feelings and "know it to be true"
I think Vader has been conflicted and confused ever since episode 3 when he feared losing padme like his mom and can't bring himself to kill the only thing that could save his wife. but after Palpatine tells him that he killed her, and he remembers her being alive. now he has nothing and he has destroyed everything and might have realized that it was all palpatine's fault, but now being under the oppression of the Dark side, he couldn't over throw palpatine, especially since he was not whole after kenobi got threw with him. so his original plan to over throw the emperor fell apart, but I don't think he ever stopped trying to get revenge for the death of padme.
This is a great discussion. sorry I went wayoff on a tangent