So hard to answer this question. Depends on what you want out of a PG. If I understand correctly, you're considering overall impact on a team. Still nearly impossible to estimate - variance depending on team.
That said, Rondo and Rose are wildcards right now. They're too hard to judge. I'd probably keep both within top 5 by default, but we have no idea how they'll return. Rose has a lower floor due to his reliance on explosiveness.
Parker has to be top 5 by default. Same with CP3. I think both are on the decline, though.
Westbrook is who he is. More of a hybrid than PG, but deserves a top 5 simply b/c he's so dominant and technically a PG. I don't think he will become much of a different player. Maybe improve with maturity, but has probably shown us what he's capable of skill-wise.
D. Will is who he is, too. I'd argue Conley as well; some will say he has improved so much this year that he hasn't reached his potential... but he was given full reigns and utilized his skill set about as well as he could this year, imo.
Irving is an absolute stud. Healthy or not, he hovers around 5-6 imo. If healthy, he will near the top of the list soon enough.
Curry is too much of a hybrid for me to feel comfortable judging. Incredible scorer, probably lifetime liability on defense. I'd rather not even classify him as a PG.
Lillard is better than Wall. Not sure Wall has shown anything to this point. Lawson is better than both (Lillard probably passes him, though).
Post by D.o.s. is better than mine, per usual, in that it's fact-based. Just my anecdotal 2 cents

Feel pretty strongly about these guys, though, and have always enjoyed following PGs more than any other position in the league.
Edit: Realize I hardly mentioned Rondo. If he comes back near his old form, I think he'll have a strong season. I've always been in the camp that he can make ANY team better and was not just the product of his environment. If I absolutely had to bet, I'd put my money on him playing at the same level on a team with a janky surrounding cast.