I say 1:45 easily. Here' why: The 800 used to be made up of mostly endurance/distance trained types with speed, that put in high mileage in training (fast milers moving down). There have been some exceptions in the past like Alberto Juantorena. The 400/800 types are becoming more common. There have been some strong 400m runners move up with success. There are also 800 runners that drop down to 400 and do quite well. Such as Hazel Clark. The 800m is 60%-40% aerobic/anaerobic. However the aerobic capactiy can be developed greatly with training, as can fast twitch type II fibers convert to type IIa fibers and take on more oxidative properties. Raw speed on the other hand can't improve nearly as much as endurance and aerobic capacity. Wariner is a 400 runner that is very light weight compared to others and has a very efficient stride, both of wich are more conducive to running the 800 than the more muscular and compact traditional 400 runners. He also has less raw speed and a slower start than most 400 runners at his level, with a PR of 20.19. LaShawn Merrit has run in the 19.8's for 200m. Having said all of this I believe there is no reason why, if he trains properly, Wariner should be able to run at least back to back 52.5-53's equaling around 1:45 800 range and possibly faster if he is tough (which is around what the top american guys do-nick symmonds may go down to 1:44