Vibraplane: Should it be loaded close to limit?

75% to 85% percent of the max load.

Sure you can work w/o extra weight.
And it still does some good for your sound.
If you're satisfied with 60% performance - than you are fine.
If you want the full benefit from your Vibraplane (read: lowest possible resonance frequency - as this is what the complete vibration isolation issue is all about), you will have to go as close to the maximum payload as possible.
Sorry - not my idea, but physic.
You may ask Audiogoner's Syntax or Solong about their journey with standard Vibraplane and then with added weight till maximum payload was approached.
They will tell you that you just can't argue with physic and how much the sonics - especially in the low and lowest registers improved.
Cheers,
D.

The vibraplane is preloaded with 100 lb, so add that to the mass of the component when calculating system resonant frequency, which is the square root of the system spring rate/total mass.

Where is all this different information coming from?
The Kinetic Systems website (which should be used as THE
information to work with!?) states a MAXIMUM OF 200 POUNDS NET @ 80 PSI for the 20x24 units. Correct?

AVphile,
The Kinetics website quotes a max load of 200, but the specification sheet for the unit quotes a max of 275. The performance graphs suggest the closer to the max load the better the isolation figures. I have emails going to both Sounds of Silence and to Kinetic Systems for some suggestions. I just thought Audiogon members who own this unit might have some insight on how to optimize its performance.