An Anglo-Russian War is a possibility in this period, IMO, due to their competing spheres of influence in central Asia. It was resolved diplomatically IOTL, but if not, war is a possibility. Like a Fashoda War, it would destroy the chances of Britain in the Entente, but I'm not sure if it would drive them to side with the Germans, with whom they were competing in a Naval Race with. As for who would win, I really don't know. I think the British have better force projection, but Russia is closer. What I find interesting is if the Ottomans decide to join the fray to turn back what was started in 1877---since that would mean Russia is fighting two powers, France would be obligated to join the war...