**When a fire and a wind jutsu of the same rank are shot by two shinobi facing each other, the result won't be a stronger fire jutsu continuing forward, but instead it'll be a weakened fire jutsu (one rank lower then it originally was).
**When a fire jutsu clash with a one rank higher wind jutsu, they will both cancel each other out. If higher then one rank, the wind will overpower the fire. However, there are exceptions; for further details continue the reading.
(Further explanation on my reasoning of the Fire/Wind clash can be found in the spoiler bellow)
The way I see the fire and wind clashing is like putting too much air into a flame, it won't do any good. However, when a wind jutsu merge from behind it only add to both jutsus momentum, reinforcing each other. I can't think of a jutsu getting stronger as he clashes with another one and loses speed. I know Fire is the elemental weakness of wind, but we shouldn't see it as fire and fuel. Air is only good for fire in certain proportion, let's not forget that.