Breakdown of Turntable Performance

Over the years I've read numerous reviews of turntables, arms, platters, and plinths.  I always wondered how much these individual components contributed to the overall sound.  Here's my take:
Cartridge - 80%
Arm - 10%
Platter - 5%
Plinth - 5%
As said somewhere above, the function of the motor and platter is to rotate the record at a constant rate, inaudibly. Other "contributions" (e.g., resonance) from platter, motor, and plinth could be viewed as defects rather than assets so ideally should be zero. The same is true of turntable support.  Once that is accomplished the rest is up to the tonearm and cartridge, correct compliance matching, and setup.  And of course the condition of the record.

Many years ago I attended a demonstration by Linn. They had two Identical Linn Sondeks, one fitted with their previous top tonearm the Ittok. The second sondek was fitted with the more expensive Ekos tonearm. to emphasise the tonearm's contribution relative to the cartridge, the Sondek/Ittok was fitted with their top mc, the 'Troika'. The Sondek/Ekos was fitted with their budget K9 mm. The cost of the Ittok/Troika and Ekos/K9 were similar so it wasn't a question of spending more money but simply what priority to give to the arm or pickup. Anyway, the majority consensus was the the Ekos fitted with the cheap K9 was sonically the winner! The Ittok/Troika was a tad more 'polished' in the treble and a bit more extended in the bass. The Ekos/K9 was superior in sound-staging, Imaging, dynamics, etc etc.

Spindoctor, That has been my experience with arms as well. The thing is... That more expensive cart on the more expensive arm (Ekos) would have brought things to an entirely higher level. It all matters. 
That's interesting, i would have bet money the Ekos/K9 rig would have better bass than Ittok/Troika one
Personally, I believe your playback is as strong as the weakest link. There is no perfect equipment . . . otherwise, there would come a time when no improvements and the industry would come to a point where their “new models” would cease. Think about it, this is never going to happen, because it would be like all disease and aging were eliminated -- how many medical and pharmaceutical companies would go out of business? You do not cut off your nose to spite your face . . . at least not among the wise and intelligent.

Let's face it, the tweaking and the updating is part of the charm and frustration of the hobby. Without it, hobbyists would have to seek another hobby to satisfy that endeavor. Contentment, as is the case with those with LIMITED wallets, would have to become a mental acceptance that there is no more updates or improvements to be had . . . perhaps all that would be left to do would be to replace that which would wear out or got damaged.