I think they both could go next year, so i'm going to go for 400m. Wariner in a year has got to improve by about 0.2 really, if conditions was better for his final he would of ran 43.3low.
Now next year America could have some astonishing 400m runners(they already have), Wariner at WR form, Merritt 43.5-6, X-man (god knows), whack in taylor or clement, im going to say clement and say he will be around 44 flat but a much better relay runner with his great strength. The WR will definately be under threat, i just hope this beijing track will be rapid like the osaka one.