There are many ways to achieve an 18 min 5k, and 6 min pace is just one of them.
If I divide 18 mins by 3miles, that's 6 mins .. so one could steady pace and run a 5k race running each mile at about 6mins and achieve an 18min 5k....now of course everyone knows that is - /+ a few seconds here and there.
I'm not sure you had your coffee yet, or you brain woke up on the wrong side of your head.
I'll agree that there are many ways to achieve an 18 min 5k, but running 6 min, 6 min, 6 min is not one of them. That would be closer to a 19 min 5k.
If I divide 18 by 3.1 I get 5:47 per mile. -/+ a lot of seconds here and there.
Look, I appreciate your input, but you are wrong. Running 6 min for a mile tempo (5 min mile PR) is not even close to the same thing as running 21 min 3 mile (18:45 5k pr). That's your 1 min rule. It's just plain incorrect.
Tempo pace DOES NOT CHANGE due to the duration of the tempo run. The best advice is to find your vdot and then look up the correct pace on Daniels table.
The guy who said to add one min to your mile PR is the next best thing. It's not perfect, but it is close for PRs under 6 min or so. It gets a little wonky for slower runners, though.
Scorpion_runner's "add one min to the race pace of the distance you are running" just makes no sense whatsoever. I'd be running slower than aerobic pace on a 5 mile tempo run if I followed that advice.