gistfile1.txt

GNU grep compiled on my MacBook Pro as "ggrep":

mranney-C02N31E1FD57:~$ time ggrep -E '^a(b|c)?' /usr/share/dict/words > /dev/null

real	0m0.020s
user	0m0.016s
sys	0m0.003s
mranney-C02N31E1FD57:~$ time grep -E '^a(b|c)?' /usr/share/dict/words > /dev/null

real	0m0.106s
user	0m0.101s
sys	0m0.004s

This is a 3GB version of "Tale of Two Cities", English language text:

mranney-C02N31E1FD57:~$ time ggrep -E '^a(b|c)?d' pg98_3g.txt > /dev/null

real	0m15.489s
user	0m14.873s
sys	0m0.598s

mranney-C02N31E1FD57:~$ time grep -E '^a(b|c)?d' pg98_3g.txt > /dev/null

real	0m53.903s
user	0m53.040s
sys	0m0.756s