You just got a lens, take your time to get to know it
No need to rush to the next big thing.
Also, I think that the difference between 50mm and 70mm is more significant than 150mm and 200mm, but this might depend on your needs. Some photographers need those extra 50mm on the long end, some need even more than that! I suggest you stick with your lens for a while, until your needs become more apparent. When you feel the lens is limiting you, preventing you from getting the shots you want, then it might be time to buy new gear.