Thanks on two accounts (the second being: reading your message, now I have an idea how to use Benchmark).

The results here confirm what you observed:

Benchmark: timing 500000 iterations of multi line, one line...
multi line: 12 wallclock secs (12.31 usr +  0.00 sys = 12.31 CPU)
  one line: 16 wallclock secs (14.64 usr +  0.00 sys = 14.64 CPU)
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