I am running this in a playground currently for testing
You should better know one thing
Playground is not a good place to test performance.
It does many, many things behind the scene at execution of each line, so your Took-time is measuring the time of such Playground efforts, not the time of `append`.
I modified your code as Command Line Tool app and tested with my Mac mini, and the result shown was...
...
5990 Took 9.5367431640625e-07 seconds for 6000 records and the count is 5991
5991 Took 0.0 seconds for 6000 records and the count is 5992
5992 Took 0.0 seconds for 6000 records and the count is 5993
5993 Took 0.0 seconds for 6000 records and the count is 5994
5994 Took 0.0 seconds for 6000 records and the count is 5995
5995 Took 0.0 seconds for 6000 records and the count is 5996
5996 Took 0.0 seconds for 6000 records and the count is 5997
5997 Took 0.0 seconds for 6000 records and the count is 5998
5998 Took 0.0 seconds for 6000 records and the count is 5999
5999 Took 0.0 seconds for 6000 records and the count is 6000
Took 0.14691698551177979 seconds for 6000 records and the count is 6000
Your code is far from efficient, but if you run it in a more appropriate way, the time would be different.