Iv found that similar tube flys that utilize bucktail work in smaller sizes, around 2-3cm long but when they get bigger there no way near as effective as larger flys tied with zonker strip.  Must be something to do with the way the material articulates in the water?  Trout down here, just cant seem to resist brown/green rabbit fur? 

Also iv gone away from heavy heads on my flys like the big cone heads and dumbells that I used to use all the time. I feel that using the appropriate sink tip to get the fly in the zone is a better way to present the fly.  That way the fly is rarely presented pointing down in the water column. 

That begin said there are always the odd occasion when using everything in your power's to get the fly in front of the fish means you have to go to a heavily weighted fly.