Running

Hello everyone, I have been running for a few months and I am currently training for my first 80km (~50miles). Once this goal achieved, I would like to train for a Marathon with a time target. My current weakness for Ultra-trail is running uphill, and I am not satisfied with my speed on flat terrain. Knowing that my aim is to participate in TORX (in 2 years, maybe), I am unsure whether I should focus on the Marathon to build up speed or continue my ultra trail training (trail, uphilll and long runs). I am also aware these are different sports and that it is difficult to give feedback with the lack of details but I am wondering what you would do and/or if my logic is flawed.

Thanks :)