Re: How to roll cast farther???
A further bit of advice regarding roll casting with a heavy fly: getting it up as close as possible to the surface will work better. You can achieve this by throwing a short roll cast to put the fly on the surface, and then performing your roll cast quickly after it.
As you're looking over pages of advice on spey casting, any mention of how to cast with "heavy tips" applies somewhat to casting with a heavy fly. In both cases you want to get the heavy item up close to the water's surface so the energy of the cast is used for airborne propulsion rather than to bring the sunk item up from the depths.