I think you should read Cathar other threads on Storm, a CSP-MAG will be within 1Deg C of other pumps.
It comes down to what he can fit, and how much he wants to spend.
As indicated, I believe the Storm required high flow / pressure, and have been recommending two MAG's in series for people that have emailed us direct.
Cathar has corrected this mis-understanding, and now I only suggest a second MAG if they really want that extra 1Deg C
I still do not have a Storm, and can not confirm directly the performance gained with higher head.