I have cast and used SDS PAGE with Tris/glycine/SDS electrode buffer.  However, I was planning to use some precast, gradient gels for the first time.  I am trying to contact the manufacturer, but I have not yet heard back.  "BisTris" is in the product description, and the catalog page mentions the possibility of ordering MES or MOPS buffer.  

My first question is whether I should change my recipe for the sample loading buffer.  My old recipe includes Tris (pH 6.8, same as stacking gel), SDS, 2-mercaptoethanol, glycerol, and bromphenol blue.

My second question is what sort of power settings should I use?  In the past I have typically used about 100 volts during the stacking portion of the run, which changes to 150 volts or more volts once the samples enter the resolving gel.

I generally do not use precast gels, so I don't have first-hand experience. But I believe that manufacturer generally recommend (obviously) their own loading buffer (LDS). While it is generally recommended to use the same buffer as the running buffer, I believe that most LDS buffer composition are also simple Tris-HCl at pH 6.8. I.e. it shouldn't make much of a difference  either way.

For power settings, I generally run at constant current as I prefer controlled and more homogenous separation (mostly as I approach this from a 2D perspective). But if your gel are the same size, you can keep the values the same (i.e. 10-15 V/ cm). But depending on the buffer the run time would change.

I am trying precast gels for the first time, and it is for a laboratory class.  I talked to someone in technical services, and he sent a pdf with some instructions.  As I read them, I did not see anything about changing the voltage between the stacking gel and the resolving gel.  I will try something similar to what you suggest.

I decided to try a test run today.  The stacking gel is only a few millimeters in length.  I started at 150 volts and about 60 milliamps, and it seemed as if the current decreased over time.  The gel ran more quickly than what I was used to.  I am destaining the gel now, and the bands look good.