@ram,
If you use the test script I put together below, you will be able to realize starting at a = 6, that set each value is more efficient .
a = 7; // Varied from 2 to 7
dt = New Table();
dt << Begin Data Update;
dt << Add Rows(10^a);
t1 = Tick Seconds();
dt << New Column("Test",Numeric,Continuous,Formula(5));
t2 = Tick Seconds();
dt << End Data Update;
Print(t2-t1);
t3 = Tick Seconds();
dt << New Column("Test",Numeric,Continuous,<< Set Each Value(a));
t4 = Tick Seconds();
Print(t4-t3);
However, it is important to note that Set Each Value can only achieve one objective unlike Formula which is much more versatile. So I don't know the exact objective of performing this comparison, but this is one way to look at it
Best
Uday