I live by the 60/20/20% rule = 60% is the butt, the first 20% is the taper, and the last 20% is the tippet. But if you need to start at 40# and end with 8# you need more than three sections, of course. What I mean is, if you need 40# to attach to that 10wt power spey head, but the fish want 8# stealth, there is no single diameter line you can patch into the middle to provide an adequate step-down. One pull and the 8# side of the knot will pop.
So you need to compound each section (butt/taper/tippet) to add steps down to the desired tippet size. A.J. McClane (my hero the ultimate fishing bum) recommends taking the first 60% (butt) and stepping it down to 60% / 40% within itself. The middle/taper can then be stepped in even proportions, and finally the tippet can be either solid (most common) or stepped down in the case of very long leaders like 15 ft spey leaders where the tippet is 3 feet long and has room for steps.
General rules I follow:
Just use maxima (except when using flouro tippet). This makes stepping down brainless and easy when your fingers are shaking as a chrome battalion moves up the rapids into your tailout during an early fall freshet. Just use each pound# rating as a step down, it works great.
Try to make the most gradual step-down possible, ideally each maxima size down. Too quick of a step-down will cause easy breakage of the leader under stress, you want to gradually step down.
If I skip line ratings in the taper, I do it in the thick stuff not near the tippet.
Then the tippet is usually a solid section. There's room for a step in spey leaders at the tippet, but you want to keep knots away from the fish's view.
Summer 14' to 8# tippet example:
So for a 14ft summer spey leader (7wt, 8wt, light 9wt spey), I usually start with 30# Maxima, step to 25# for the two pc butt. 60% of 14 feet turns out to be 100 inches, so that's easy - 60" of 35#, 40" of 25# maxima.
Then 3 steps in the middle at 11" round it to a foot (20#, 15#, 12#) each for a 3ft taper.
From 12# I can tie either a 10# tippet or an 8# tippet without a radical step-down, in fact 12# flourocarbon (sight-free or another very good brand) is as thin as 8# maxima, super-strong and less visible so I'd recommend that for summer work.
Big water dry leader example:
For a 15' leader for bigger dry lines (e.g CND 14, 15', 15'6", 16'7", spey) I start with the level tip cut off the flyline for most brands and use a 40# butt tapered to 30# (60/40 of 60%) in the first section from line to taper. 60% of 15 feet is 108", so there is plenty of room to step down if you want something other than 12# tippet.
Then the taper is 25#/20#/15#
This accomodates a 12# tippet or a compound 12#-10#, or 12#-12 flouro works very well for a step down.
If I need 15# tippet (thankfully there are fish in this world that require 15# dry tippets!) the taper is stepped only two sections deep and the 15 becomes the tippet full solid length.
Sinktip Example:
For sinktips, there is no need to tie a fancy leader. I would agree with many who say you only need a piece of straight 15# for winter tip work, about 4-6 is my preference.
Nonetheless, when using light tips in summer I prefer to use the cut ends of S/A shooting heads in types II, III and IV with a tapered leader of 6-8 feet starting with 30# butt tapered down to anywhere from a 15# to a 12# flouro tippet, never less than that for tippet with a tip. This makes for pleasant casting and the flies are smaller and lighter in summer, making presentation more subtle in low water, etc.
Other notes:
Some guys cast so well a straight shot of high quality leader material is all they need to make fantastic casts and catch fish. I tried it and found it doesn't make a huge difference whether the leader is precisely tapered or not if you make a good spey cast.
I on the other hand and not in this league and would rather have the highest possible test leader for my wind knots possible! I broke off a huge steelhead due to a wind knot in a solid 15ft 15# leader least fall.
I guess this is one of the rewards for becoming a great caster - you don't need to tie tapered leaders for spey casting once the casting can always "fill the sail" cast after cast. I'll get there...
