"Is there any situation where a PE would sound bad on a given circuit?"
Of coarse there is, its all about interaction...this is why we supply many different models, just because one model doesn't sound good on a circuit doesn't mean a different model will have the same reaction. It all depends on how the filter saturates the circuit vs. the location of the system. There are multiple different parameters as to why product A sounds different than product B installed here vs. there. It could be as simple as no in wall cable staples prior to outlet A vs. 35 staples prior to outlet B on the same circuit. Keep in mind all the different ringing parameters between point A and B to get an understanding of how to properly tune a circuit. Pluck a guitar string and watch it vibrate, the in-wall wire does the same thing except at a lower frequency. If you can adjust the sound of a individual string by altering your hand position against the fret, the same is true for the in-wall along the entire length of the circuit. Just like a guitar string, some locations will harmonize better than others.
If the circuit rings bright because of added resistance then use a warmer filter. If the circuit becomes dull because of added inductance then try to raise the impedance using a choke...a 193L is a good choice. Balance is key to proper circuit tuning.
"maximal surge protection, noise suppression, etc., occur when all circuits in the house are treated with a PE of one type or another, in effect turning the entire circuit breaker into a huge line conditioner."
Maximum surge protection occurs when all circuits harmonize with each other. Usually that means a filter/s should be installed on all open circuits. A surge is a high frequency EMI magnetic field, the standard PE circuit neutralizes stray EMI, but you need a decent amount of coverage throughout the home to neutralize a lightning surge. This is a different approach from normal surge suppressors tripping the breaker, the PE attempts to eliminate the surge potential between the different installed filters...each filter attacks the surge current and lowers the field over distance.
"Also, would it be a good idea to put a standard PE on the same circuit (different outlet) as a Ref II if that circuit seems to benefit from the Ref II (it also benefited from a 193L, but that came out when the Ref II went in)?"
As long as the two harmonize together on the same circuit it's fine...you could even add several, don't be locked in to typical standards, you are trying to fine tune numerous harmonic points on the same circuit.
