2800 is probably a good baseline when running the cleaner. How many hours per day does it run at this rpm? Maybe 4 hours are 2800rpm will be sufficient to clean your entire pool - but only you can tell if that's too long or not long enough. So, see if 4 hours is long enough and adjust up/down as needed to clean the pool to your satisfaction.
The rest of the run time can be at 1000-1200 rpm. That will reduce the electrical usage during that run time by a bit more than 75%. General rule of thumb is reduce the rpm by 1/2 which reduces the power consumption by 3/4. At 2800 rpm if watts/hr were 2000, at 1400 rpm watts would be about 500. As you can see, if you reduce the rpm by 50%, you can run the pump at that rpm twice as long and still save 50% of the electrical cost.
You need to run the pump at a high enough rpm to efficiently skim the pool surface. Many pools can run at 1000-1200 rpm and attain that.
