Surface stability is subjective, and would best be discussed over the phone due to it's nature. For now, keep this in mind: all matte surfaces, including fine art and watercolor papers, are fragile and show marks relatively easily.
Texture can be divided up into three areas: Smooth, Velvet, and Textured.
Smooth. Smooth fine art paper is not completely smooth. It is smooth relative to other surfaces, but it always does have the slightest texture or "calendering" to it. But for all intents and purposes, the smooth watercolor papers are smooth.
The following are smooth papers:
"Thickness" can be determined using a micrometer, and many papers are defined by a thickness in mils (one thousandth of an inch). However, the most useful and universal definition of a paper's sturdyness is given in terms of its weight.
Weight. Weight used to be given in pounds (lbs) per ream (or roll) of paper, but that was a very arbitrary definition as rolls & reams were different sizes.
The "in" way to define paper is in terms of the grams it weighs per square meter (gsm).
Cardstock Thick is anywhere from 350 to 500 gsm. These papers generally cannot be rolled! This stock is more expensive, and must be purchased in cut sheets. It is more expensive to ship as well, because it must be shipped flat. You'll noticed that most of these papers end with (sheet stock) this is because they also come in a cheaper, thinner, roll stock.
Also, if you are considering ever purchasing these papers for your own use, they are too thick for most desktop printers made before the year 2003. Only printers with straight feed slots can handle them.
Papers that are 350 to 500 gsm:
Thick Stock is anything from 225 to 325 gsm. These papers are just as good as the sheet stock, only thinner so they can be purchased in rolls. This makes them more economical to make and ship, saving you money.
Papers that are 225 to 350 gsm: