Largely correct. Actually, I have seen a lot of estimates of flies' speeds to be about 8kps, but in one situation as a boy, I tried to put that useful fact into application to lose some flies that were pestering me. Now, I can actually run faster than 8 kph, but on this occasion I happened to be on horseback. It was a pretty sluggish horse, but she must have been exceeding 20kph and I had the vivid experience of watching a fly in mid-air keeping pace with me , apparently comfortably settled into position about a foot to the right of my face (there was accordingly no question of its being entrained in an eddy or the like!) So beware of estimates of maximal flight speeds of insects!

However, insects are small, springily constructed, and strong in proportion to their size and mass. It takes a bit of doing for them to hit a plain surface hard enough to come to harm. Houseflies swatted out of the air may fall to the floor, apparently dead, but unless you then step on them, a goodly proportion of them recover in a few minutes and soon take off again. High speed vehicles are another matter. Even at a modest 100kph you can pick up a lot of midges and moths on your headlights, not to mention  the odd anonymous yellow blob.

If otoh you accelerate them to really high speeds, perhaps a couple of hundred kph,  by sucking them up with a vacuum cleaner, then flies demonstrate their mortality dramatically as soon as they hit the other side of the bag. The only traces you are likely to find are the red splashes of their optic pigments.