If you have to turn around prior to the PNR, would you rather have a large and likely increasing tailwind or a small and likely decreasing tailwind ?
I would take a view of the overall wx pattern. There is no simple answer. The way you pose the question has no practical meaning.
The accuracy of a forecast varies widely according to the weather. So e.g. The light winds prevailing within a large area of one or multiple high pressure zones are basically unforecastable. They may all be within 10kt but nobody can tell which way it will go and at what altitude. Same with a region of multiple (but weak) lows. If you have an aggressive frontal system OTOH then the situation is better defined but the winds along a route are much more sensitive to timing because the whole lot is likely to be moving at some speed, and forecasters routinely get the speed wrong i.e they forecast the wx ok but for the wrong time.
For me, the only way is to disregard tailwind (unless there are so many alternates along the route that it is moot) and take the worst case headwind as constantly present.
In the TB20, this policy makes Crete easily reachable from the UK with one fuel stop somewhere nice. If one took tailwind into account one could do all kinds of things and possibly LGST would be reachable nonstop (1450nm) but none of the alternates have avgas so if you screw up.... Not all that different to this ferry flight really except there was not just no avgas but no runway too.
But then i dont ferry to Hawaii
