Thanks all for your suggestions. By using Benchmark and Compress:Zlib on 10 files (each about 47K each), I found the following:

pre compress::zlib:

the code took:17 wallclock secs (11.76 usr  2.52 sys +  0.25 cusr  0.2
+5 csys = 14.78 CPU)

with compress:zlib:

the code took:15 wallclock secs ( 9.71 usr  2.60 sys +  0.02 cusr  0.0
+6 csys = 12.39 CPU)

Not much of a difference, but for more files, I found the
saving in time up to 10 seconds.

Thanks once again!

Regards,
    Stacy.
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