I have yet to try the 73ft and 83ft Equalizers ... rivers in my area have just thawed out.
I was quite happy with the 70ft Clearwater Touchdown heads. My 16' 8/9/10 Highlander could easily tame both the 9/10 (802grains) and the 10/11 (864grains) versions. Like Bruce mentioned, it's all in the taper and grain distribution. With longer lines, there's a bit more play.
Something to consider from Bob Meiser's website (Balanced Rod/Line Marriages):
~ Classic Speys
Many traditional two handed anglers feel that the true poetic beauty of delivery will be best achieved with the use of a longer bellied Classic Spey line married to a long rod. I fully agree with this, and I will always pause my fishing day to watch, and admire a skilled long line caster.
One of the major advantages of Classic Spey lines that anglers universally appreciate is that in order to successfully fish many of their runs, they need only to present, swing and re-deliver the lines long belly length, this minimizing the need to strip in long lengths of running line at the end of every delivery. Shooting heads (on the other hand) have much shorter head lengths, and each delivery will require the striping in of a substantial length of running line.
Rule of thumb: Classic Spey line belly lengths will generally be 4 to 4.5 X the rod’s length. A long line caster delivering a 14'0” rod will feel comfortable with 55' to 65' of aerialized line grain beyond the rod tip. A 13'0” rod will like 50' to 55' etc. Their preferred grain weights will be similar to that of comparable Skagit on the same rod. For example: If your 14'0' 7 wt rod performs well with 650/675 grains of Skagit and tip … I would suggest a Classic Spey of a similar grain weight = 650/675 grains.
Another way to approach the marriage of a suitable grain weighted Classic Spey would be to use the rods determined grain window. If your 14'0” 7 wt has a grain window of 450/750, the happy spot for most classic Speys will be around +- 100 grains down from the high end of the grain window = +- 650 grains.
Most well designed Classic Speys will have the ability to carry both conventional tapered mono leaders, and poly coated sinking leaders with equal efficiency. The most versatile will be those long belly lines that will have the ability to carry not only mono and poly leaders, but also have the ability to carry various sink rate tips as well.
I've used this as a "Rule of Thumb" and it works very well for me, gets me right in the ball park anyways. Feel for loading is always personal and grain weight is certainly a factor, however a well designed taper and proper grain distribution makes all the difference.
I'm very excited to try the 54ft, 63ft, 73ft and 83ft Equalizers on my various rods. I am highly impressed with the Touchdown series, EMT, EEMT and the 15M Extended Spey Heads. Everyone has been telling me, "Wait until you try these" ... makes me wonder if it can get any better ... like I said, I'm excited
Just to answer your other question, I had no issues with 10ft and 15ft polys (all densities) right off the end of the Touchdown heads. Long mono leaders are a dream right off the end.
Incredible turnovers !! The line/leader is fully extended before it touches down ... makes for excellent presentations