Personally I prefer to get some armor across the Daugava as soon as possible and occupy Riga (it will only serve as a supply source once access to the Gulf of Riga is secured, right?) since it gives a bit more flexibility for he next turn and might threaten to create a small pocket.
I think displacing the infantry at the river Dubysa might be a good idea in order to make rail repair there faster for the next turn.
What do you think?
