Even then, the less alternations you have the faster your regex will run. Of course if the strings or patterns have nothing in common it makes no difference.

I did a quick test and got the following results:

                 Rate       Raw Regex Assembled Regex
Raw Regex       614/s              --             -9%
Assembled Regex 676/s             10%              --
[download]

The text to check was part of a play by Shakespeare, loaded into an array (1 line per element) and the regex used was

qr /this|that|here|there|where/;
[download]

Assembled into a more efficient regex it looks like:

qr /(?:th(?:ere|at|is)|w?here)/
[download]

Even by eliminating only ONE of the alternations (5 vs 4) a 10% speed-up was obtained.

PS: I do not know about 5.10, this was tested in 5.8.