Keygrip - i'm not really clear what your question is? The extra fuel required to carry 'extra' fuel is ALWAYS a factor in relative terms. Whether it becomes 'significant' depends on your finances. If you can easily absorb the cost of around 4% per hour of the extra fuel you are going to carry, it matters not a jot. In a one-off trip in a 150 it is unlikely to be 'significant'. Carrying 8 gallons extra on every 1 hour flight, and flying 6 hours a day every day.......? That's around 2 extra gallons burnt every day, or getting on for 700 a year. Is that significant?