Loops are slow in GAMS

When optimizing GAMS code it is always worthwhile to see if you can remove loops. Here is an example of an if,then,else construct:

   1  set i /i1*i200/;
   2
   3  alias (i,j,k);
   4  parameter a(i,j,k),b(i,j,k),c(i,j,k);
   5  a(i,j,k) = uniform(0.1,1);
   6  b(i,j,k) = uniform(0.1,1);
   7  c(i,j,k) = uniform(0.1,1);
   8
   9  parameter p1(i,j,k),p2(i,j,k),p3(i,j,k);
  10
  11  * this is fast
  12  p1(i,j,k) = ifthen(b(i,j,k)>0.5,a(i,j,k)/b(i,j,k),c(i,j,k));
  13
  14  * this is slow
  15  loop((i,j,k),
  16     if(b(i,j,k)>0.5,
  17        p2(i,j,k) = a(i,j,k)/b(i,j,k)
  18     else
  19        p2(i,j,k) = c(i,j,k)
  20     );
  21  );
  22
  23  * this is fast but I feel uneasy about assumption that
  24  * these conditions are quaranteed mutual exclusive
  25  * for floating point numbers
  26  p3(i,j,k) =  [a(i,j,k)/b(i,j,k)]$(b(i,j,k)>0.5) + c(i,j,k)$(b(i,j,k)<=0.5);

The profiling info clearly indicates the loop is the slowest alternative:

----      1 ExecInit                 0.000     0.000 SECS      3 Mb
----      5 Assignment a             1.762     1.762 SECS    261 Mb  8000000
----      6 Assignment b             1.748     3.510 SECS    518 Mb  8000000
----      7 Assignment c             1.747     5.257 SECS    775 Mb  8000000
----     12 Assignment p1            3.307     8.564 SECS  1,032 Mb  8000000
----     15 Loop                    22.027    30.591 SECS  1,288 Mb
----     26 Assignment p3            3.900    34.491 SECS  1,545 Mb  8000000

I prefer the ifthen construct as this has a real 'else'. The assignment to p3 uses two different $ conditions, which makes me feel uneasy.