I worked up a load for my 280 with 7828, switched to ssc when I ran out, didn't see any difference with the same charges. SSC definately has better flow characteristics.
The two have the same burn rate, but different densities. 7828 takes more volume for the same weight of powder. You could have trouble if you had a favorite max load of 7828SSC and tried to substitute 7828. The increased powder volume could cause excessive pressure.