JC3+ With Kleos SL?

65db of gain equates to 1778 times V. So 0.25mV of cartridge output becomes ~450mV.
64db of gain equates to ~1600 times V. The 0.25mV output is amplified to ~400mV.

Unless you’re using a passive linestage, you’re going to end up with ~4V of signal given 64 dB of phono gain, which is more than twice the signal voltage needed to drive any amplifier to full output .

 Of course, I would never pretend to challenge the knowledge level of anyone like Jonathan Carr, when it comes to this subject. However, please show me where Jonathan Carr ever wrote that 65 DB of gain was good but 64 dbof gain is not good. Thanks. 

I repeat: Driving a phono stage capable of 65 dB of gain with a cartridge that puts out 0.25mV under standard conditions is not per se “stress”-ful. I don’t suggest that you didn’t hear what you heard. I do think maybe there was some unknown factor that affected your results. In general, I agree with you that ideally you want all components to operate within their comfort zone. Or maybe you were picking up RF, etc. There are many possibilities.

Davey, You cannot be sure that your "gain" problem centers around the gain of your phono stage (65db per your report) and the output of your cartridge (0.25mV).  The subjective impression of gain also depends upon the input sensitivity and gain of your linestage (if you drive a linestage via your phono stage) and the input sensitivity of your amplifier(s), assuming other evidence that the amplifier/speaker match is copacetic.  On paper, a cartridge with a real output of 0.25mV driving a phono stage with 65db of gain should be fine.  I am currently using an Audio Technica ART7 (less than 0.2mV output) into a Manley Steelhead set at 65db for gain.  The Manley output stage adds no further gain, and there is absolutely no sense of strain or noise due to stress.  (The Manley drives a pair of Beveridge direct drive amplifiers which have a solid state input stage; I do not know the input sensitivity, but obviously it's adequate.)

By the way, for the purposes of discussion, at least, it's best to separate "distortion" from "noise", I think.  Your lumping of noise and distortion is not wrong but maybe a little confusing.  Noise of the kind you describe is accounted for by the "signal to noise ratio" specification, which is usually stated separately from harmonic or IM distortion measurements.

Keep in mind that the rated output of a phono cartridge is only a representation of what it does at one particular stylus velocity (3.54 or 5.0 cm/sec). When you are playing actual music the stylus is moving faster than the standard velocity most of the time. Therefore the actual output of that cartridge while playing music is going to be greater than its rated output most of the time. And the difference between 64db and 65db is of course trivial. In other words, no problemo.