A recent look into my own signal quality on PSK made me take a search on the net for information on PSK signal quality.
I came upon this web site (link) which is a site concerned with
"This site is devoted to promoting RSQ as an improved signal reporting system for narrow band digital modes and to demonstrating its application to the popular PSK31 mode."
To this end, they recommend and point out that Regions 1 and 3 have adopted the following
Readability (% of text)
R5 95%+ Perfectly readable
R4 80% Practically no difficulty, occasional missed characters
R3 40% Considerable difficulty, many missed characters
R2 20% Occasional words distinguishable
R1 0% Undecipherable
S9 Very strong trace
S7 Strong trace
S5 Moderate trace
S3 Weak trace
S1 Barely perceptible trace
Q9 Clean signal, no visible sidebar pairs
Q7 One barely visible pair
Q5 One easily visible pair
Q3 Multiple visible pairs
Q1 Splatter over much of the spectrum
Seems very reasonable to me and will become part of my operating practices.