interesting that people put more value on F as a daytime flight than nighttime.....I grabbed a CW reward ATL-LHR a while back and then on the return it was F or WT+. The actual $ cost was only $30 more ..miles 75000 v 45000 but as I have shed loads that's no worry.
So I have the overnight in CW and return in first which seems to be the mode of choice