If you're not fishing a Poly Leader on your floating Spey lines, you should be. They help turn over your fly, especially when making shorter casts. Plus, a Poly Leader give you more "grip" on the water when forming your D-Loop. More so, you can buy them in different densities from floating to fast sinking giving you a lot of flexibility in your dry line fishing.
Although Poly Leaders work great out of the box, you can get a lot more miles out of them with a simple modification. Using 20 pound Maxima, tie on a 1' butt section using a seven turn Albright Knot. Finish the other end of the butt section with a perfection loop. Loop your 2' to 4' of tippet on using a triple surgeons loop and you're ready to roll.
I've seen some leaders start to delaminate when an angler accidently places their fly into a tree and pulls like hell to get it out of squirrel land. By doing so, the core material can separate from the polyurethane coating. The Albright knot will displace the pressure equally on the core and coating. It's a great trick to make your Poly Leaders last a long time.