The rule of thumb i have heard from is 2 secs per pounds per miles
Is there any bigger for slower runners like 2.6 s /lbs/mile?
For a 30min 10k runner who loses 3 kg which is 6.6 pounds
That is : 6.6 pounds x 2 s x 6 miles = 82.69s
That translates to 28m37s 10k
What a big improvement!