I've on G5 and it's my 1st fair weather chocobo. And as someone mentioned before, I've been on the receiving end of a heavy whilst on a foul chocobo during rain. It only slowed me down to their pace, and as we were going the same speed, I stayed ahead. This was one of the later birds, so I assumed it was the results of breeding (better stats, high max speed, etc), or being a higher level. Either way, regardless of weather, I could sprint the entire length of sagolii/costa and I'd rank high unless I got badly screwed over during the race. Rain seemed to be a rarity (anecdotal).

Now though, as I've said, I'm on my first fair weather, and I've noticed what a huge difference the weather can, and does make to these birds. Also, anecdotaly, it seems to have brief showers in nearly every race at the mo.

On a side note, does anyone know if prefering foul weather is hereditary? Because if that's the case, then I'll just breed my foul weather chocobos with each other.