is there a rule of thumb on sink rate? 1' per sec? 3' per sec? 1/2 oz? 1 oz?

There is no "rule of thumb" on sink rate. Some times a slow fall is what makes them bite, some times a fast fall is what is working. I hate the expression " let the fish tell you" but in this case it's true. Generaly, but not always, cold water= slow fall, warm water = fast. Water clarity is a factor as well, in clear water some times faster is better so they don't get a real good look at it reguardless of water temp. Lots of things go in to adjusting the rate of fall as well, line size and type (baits fall faster on thinner braid then thick mono or fluoro), sinker size, bait type (a senko with a 1/4 oz pegged to it's nose falls like a bullet, but a 1/4 jig with a bulky trailer "floats" down) HTH