As to the wind...well, asked my QFI that too and the answer was straightforward...its not an issue because you will even out fuel useage during the navex...ie on the southward leg we may have a tailwind...therefore use less fuel...so use more fuel on northward leg back home due to the headwind but we have more anyway because we used less than calculated because of the tailwind on the outward leg - seems logical to me! Groundspeed? I'll have to ask about that one!
I suggest that you be very careful with this assumption.
For example:
TAS 100 kts
Distance A – B 100 NM
40 kt headwind out
40 kt tailwind home.
IN STILL AIR CONDITIONS
Outbound time A-B is 100NM / 100 Kt = 1 hour.
Homebound time B-A is 100NM / 100 Kt = 1 hour.
Total time is 2 hours.
IN 40 KT WIND
Groundspeed out = 100 – 40 = 60 kts.
Outbound time A-B = 100Nm / 60 kts = 1.667 hours.
Groundspeed home = 100 + 40 = 140 kts
Homebound time B-A = 100Nm / 140 kts = 0.714 hours.
Total time = 1.667 + 0.714 = 2.381 hours.
Multiplying the extra 0.381 hours by 60 converts it into 22.88 minutes.
That’s an increase of 19% in flight time and fuel used.