To add to what Hal said…
DWS example, there are 4 16″ sizes available with a measuring rim width of 7″, which is: [i]the industry standardized rim width upon which the tire must be mounted in order to confirm it meets its dimensional targets[/i]. This is what Hal means by “too wide will move around on the rim.” Stick with a tire with a measuring rim width that matches your rim width.
Of those four tires, the 205/45/16 is the smallest diameter = more revs per mile. This effectively raises your rear diff ratio without taking the point hit.
http://www.mysporttrac.com/mysporttrac/projects/TireSizeChangesAndGearing.pdf
This is good for autocross. If this is the way you want to go, looks like the Conti is your only choice in that size.
On weight, it is a good thing to consider as well. I believe the general understanding is, one pound of wheel/tire (unsprung weight) is about the same as 8-10 pounds of sprung weight. Our classification system does not consider wheel weight = free weight savings. My stock wheel/tire combination weighs approximately 53# per corner, but what I run for a/x is approx 42# per corner. Do the math. 🙂
Treadwear ratings are only comparable to tires by the same manufacturer. A 540 rating on a Conti does not equal a 540 on a Bridgestone or other make. This number is pretty useless other than to compare a 500ish to a 100ish, obviously the 100ish is a stickier tire. But, a 140 on a BStone compared to a 180 on a Conti doesn’t necessarily mean the Conti isn’t as soft or will last longer – too close to compare like that.
Tire Rack has a boatload of tech information on their site: http://www.tirerack.com/about/techcenter.jsp