The 135 with SAS is ok, reduces the workload in comparision to the 105 . But for flights over open water I would prefer ATT, 4 axis AP with RadAltHold would be the optimum.
In smooth weatherconditions SAS is sufficient, but workload increases when it gets bumpy...
Most of my time (~2900h ) on 135 was SAS only... My offshore experience was with 3 or 4 axis AP equipped machines of different type
skadi