One thing to remember Ralphie is the temp/humidity too. I too have struggled with this runtime issue with both .12 and .21's. I noticed on the hot summer days like when you where running your 4 it is harder to make time. I believe you are getting slighty better mileage with you 5 but I think when it gets hotter in the summer time you will be struggling to make time even with your 5. One other thing I found that has saved me fuel is throttle control. On a long straight away I have found there is not a difference in speed if you don't smash the trigger all the way back. Anywhere between 1/4 and 1/2 throttle will give the same speed but less fuel burn.I didn't believe it myself until I tried it.