Onhwy61 makes some excellent points.
Although I would differ with his last statement that it is virtually impossible to compare different designs. However, it can be rather cumbersome considering what is entailed with swapping out racks.
Its also important to note that some racks take up to 8 days or more before a settling-in process occurs. Some racks need no settling-in time at all. For some racks that require a certain settling-in time period, its like a light turning on in a room once that settling has occurred and its entirely possible for improvements to continue well beyond that.
Still other racks can mightily impress with performance gains right out of the box and then still mightily impress you again after the settling-in process has occurred. Of course other racks offer no performance gains at all or can sound worse than what you were using previously.
Without knowing about a settling process, one could easily draw the wrong conclusions of a given rack's performance. Even moving some racks just a few inches may force the settling-in process all over again. The manufacturer should be able to give you some insight if a settling-in process applies to their products.
It may help to re-iterate that there are two main methodologies regarding vibration control, mechanical transfer (aka coupling) and isolation / dampening (aka de-coupling). A third type is somewhat of a hybrid between the coupling and decoupling methodologies where the mfger decouples certain portions of their product while coupling other portions of their product.
With that in mind, you may consider holding off making your rack selection until you are confident determining from your own research (then determine from the manufacturer's design perspective) which source of vibration induces far more sonic harm than the other two.
The three primary sources for vibration include floor-borne, air-borne, and internally-generated (transformers / power supplies, motors, etc. within the component itself).
Understanding or misunderstanding which source of vibration induces the most sonic harm will certainly have an affect on the design, execution, and especially the performance if the source of vibration determined to be the most harmful turns out to be wrong.
Simply because dealing with vibrations already captured by the component may require a completely different and quite possibly opposing methodology used to keep vibrations from ever entering the component in the first place.
In the end, there is no reason not to expect the performance gains of a properly designed racking system to impress you no less than a major component upgrade.
Then you get to it all over again when you address the vibration control issues of your speakers. :)