I'd go back to the plan if possible, but that's maybe just me liking to have clear instructions to follow! As for speed, there's no 'right' number - if you could manage to hold a conversation but not sing, then you're working at the right level. If you think you could manage a bit faster, you could always do the first couple of runs at today's pace, then speed up slightly for the last few and see how you feel. If at the end you still feel you could have gone quicker, then try the quicker speed from the start of the next run.
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