If you were to lager that Dortmunder for 4-6 weeks would it capture that creamy lager texture you speak of?
I can only go by what I've tasted from true lager brewers and I'd say yes, much creamier mouthfeel when lagered.
What do you find the peak of the Dortmunder to be?
Mine starts out a little hoppy so it takes about four weeks to reach it's prime but it's very drinkable on day 15.
Are you pitching that 833 at 50 as an active starter (old wort decanted and fresh 50 degree wort replaced until krausen is achieved in the flask?)
On brew day (night actually) I pour the still "beer" off the starter and replace it with some of the wort I just made. I put the starter into the same 50F space as the fermenter and pitch the next morning when the starter is active and at 50F like the fermenter.
Will the peak of that APA still be in the 5 week range?
Yes, although quite drinkable early, it's better when about 5 weeks old.