Re: DEEP and FAST nymph rigs?
You might want to consider getting 5X leaders and then add the 2ft of 6X. This gives you the flexibility of having the 5X for fishing a little larger fly but you can still drop down to a liter tippet if the fishing conditions call for it. Since you stated you are adding the 24" of tippet for deeper water that tells me you are fishing subsurface. You don't need as light of a leader when fishing subsurface. You could probably get by with a 4X just as well as a 6X.