Long ICs - A'gon versus Audiocircle

Tony, it depends on the output impedance of the source. You will have roll-off issues only with high impedance output drivers.
There are other issues with long wires, which have mainly to do with noise pickup, as you know... The noise issues are much less severe with speaker cables. That is because noise in interconnects gets amplified and noise in speaker cables just loads the speakers, possibly interacting with the amp, but in general it does not get amplified by the electronics.
Short interconnects rarely need shielding for noise/hum reduction. Long ones rarely get away without proper shielding. So, lots of reasons to go with a "traditional" short IC/long SC.
BTW 12-16 pF/ft is not typical. Check specs more carefuly!

You may use a Zobel on short speaker cables too. In theory it is a circuit that only terminates RF energy, way above 20 KHz.
Nsgarch: I don't agree with the argument about damping factor with tube amps. Most of these amps have a high output impedance to begin with and the great majority has long thin wire in their output transformer. A more reasonable statement is that long speaker cables should be made of thick (effective) gauge. BTW, that concept is also debateable, given the crossover components in some speakers.

As for balanced vs. unbalanced, not all pro audio gear is great. The requiremets in a production facility is first of all reliable operation. A "rat's nest" in a studio would be Hell to resolve without balanced wires, so sacrifices are acceptable.
That is not the same for the home system, which in many cases is much more refined than pro audio setups. That's because the home user can afford down time and fiddling with the setup with endless upgrades and tweaks and the studio engineer can't.
While touching on this subject, many people mistakenly assume that studio equipment is great for the home. The requirements of a mixing session are not to enjoy the music but to tell the miniscule details in a near field environment. There might be more rigid need for low distortion at very high SPL, which means nothing to the home user. As we all know, there is no free lunch in engineering.
The home user would do much better buying equipment designed and optimized for home listening, not for pro audio applications, IMHO.
You may have to deal with all sorts of hassles, like hum and other noise and compatibility between devices and cables, but in the end you could reach an optimal "point solution", that is really the best one can dream about in an audio system.
It's sort of like buying a Honda Civic vs. building a tuner Civic... The basic car has great performance and a warranty - it's a safe design. The tuner car may be uncomfortable and quirky. It might die at stop signs and idle rough on hot days, but in the end it will be better on what it was optimized to do - go fast or race...
The same with an audio system. You can play it safe and have a pretty decent performance, but to reach the summit you really have to work harder... With enough will and preseverence, you will eventually make it...
My very subjective opinion, of course.