I doubt Unit's gonna hit 5000 Ks for his career. I think he IS capable of throwing 200 Ks a year for another five years....if he was to be healthy. But I don't see him lasting another five years, despite how strong he looks right now. He'll go another three years, then call it a career. I think he will go down as the greatest southpaw in history, though.
As for the 50/50, I don't know if Soriano will do it. But if he does, it won't be before Vladimir Guerrero. The guy is totally insane, with stats busting out of every pore. And that's going to continue for years to come, barring injury.
I don't think this is a milestone thing, but I'll throw it out anyway. Do you think Ken Griffey, Jr. will make it to Cooperstown if he doesn't hit 600 HRs for his career? I think he's going to get to that mark, but let's say he has to retire before making it due to injury. Will he get into the Hall of Fame? I think he still would, but it might depend on if he's key in winning a Championship or not.
And going off that note...do you think 500 HRs is still an automatic ticket to the Hall of Fame? I don't think it will be, in the near future, considered an automatic. I think 600 will become the new gold standard for HR hitting Hall of Famers.