Is my thinking correct to see the only big difference in the two unit would be that the SDS can be programmed for more advanced curves?
Much
less advanced curves.
Get a copy of Nigel Speedy's recent Kitplanes article titled "The Effects of Ignition Advance on Cylinder Head Temperature, Speed, and Efficiency" (June 2017). Nigel is a professional test pilot, who put a lot of time and money into finding his optimum ignition timing for both best power and best economy mixture settings. It turns out that best power, as you might use for climb, requires little or no advance beyond the fixed setting specified by Lycoming, Superior, Titan, etc. The data says the pre-programmed ignition systems are wrong; when you try to use the expensive horsepower you bought, all they do is increase CHT. They advance when advance is not wanted or needed.
There is benefit to significant ignition advance when mixture is set LOP, up high. Even so, Nigel notes that running fixed timing and simply climbing to a higher altitude can result in near equal efficiency....with lower CHT.
Higher altitudes are easy when you don't fight CHT in climb.
Mike Robinson has done a fair bit of ignition test flying also, and can tell how closely his data compares with Nigel's. If I ever find time to return to experiments, I intend to gather a similar data set for an angle valve.
There are only two systems which allow programming
dual ignition maps (one for best power and one for LOP),
and changing between them in flight with a single switch flip, SDS and Ford/MegajoltE. Only the SDS is self-programming; the EDIS/MegajoltE requires a laptop. And as noted, the SDS system now switches to the ROP map automatically above 25".
Nice one Ross.