Thanks to an excellent piece of advice I read on here somewhere I swap an 8T cargo rack for a fuel scoop
So, assuming you can refill at maximum rate, you are spending 3m1s refilling, according to http://www.edshipyard.com/#/L=305,mpV5QG5QG,2-BkAA8c72BkAA8I,08c08c7Uw072mpU2Uc4zM02M
If you can run a leg in 6 minutes, those 3 minutes wasted could on average net you half a cargo hold worth of profit. Plus the 8-10k you could have got from the 8T you replaced with the fuel scoop on that particular run.
Hard to judge if the scooping nets you more profit, or less. My guess is that doesn't matter much, so I don't bother with the re-outfitting every 3 runs or so.