Well of course the idea that a certain brand of helmet is going to make you faster is kind of silly for nonprofessionals- but then again noboby here was claiming it would!
I'm no racer (more like a snail) and I have not run into people who blame poor racing performance on their cranks.
All I know is that stuff like heavy winds and extreme cold will most certainly slow ME down. Winds can be good to push against though, for the extra workout.
It's probably just as challenging to ride in 100F temps as it is to ride at below 30F. Some people do better in one over the other. I'm not quite sure yet whether I do better in extreme heat or cold. I do pretty well in 35-45 degrees, and I enjoy it. However, if I'm going to ride in sub-freezing cold I have found I need some pretty heavy duty layering to keep from freezing especially if I am out for several hours. An hour is fairly easy to keep warm in though.