Australia has a mulitude of fast flowing streams and parachute hackle flies are frequently used. Especially during Baetid hatches. I know there are a lot who will argue that your hackles should be longer than the size of the hook that you are using. But practice over here has found to question those thoughts.
It should be remembered that one of the first things that come into a trout vision such as a mayfly as it heads towards it is its upright wings. It is for this reason many of us will tie our posts a little longer and use a hackle a little shorter than standard to help feature the post. To me it is all about balance and holding that post upright.
I don't know if you are aware but when Parachute hackled flies were first released for sale by the House of Hardy in England they actually called them Ride-Right flies.
I suppose that makes us think a little does it not. The bottom line is if it looks good to you then that is the most important thing. Testing fly styles for your waters is a lot of fun and you learn a lot.