If you had sailed any slower, (in the past) the war would be over (now, in the present. We would be in a state of peace). If you had sailed any slower, (in the past) the war would have been over (by now. The war would have ended before now).
There is little practical difference in meaning.
24 hours after the war ended, we can say: The war is over.
The war has been over since yesterday.