Even excluding IO, I cannot discern any appreciable difference either. @words contains 178,000 words:

[0] Perl> $c =0; $t = time; m[(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] and
+ ++$c for @words; printf "Found $c matches in %.5f seconds\n", (time(
+)-$t);;
Found 1905 matches in 0.14288 seconds
[0] Perl> $c =0; $t = time; m[(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] and
+ ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.12593 seconds
[0] Perl> $c =0; $t = time; m[(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] and
+ ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13659 seconds
[0] Perl> $c =0; $t = time; m[(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] and
+ ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.14437 seconds
[0] Perl> $c =0; $t = time; m[(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] and
+ ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13993 seconds
[0] Perl> $c =0; $t = time; m[(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] and
+ ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13856 seconds

[0] Perl> $c =0; $t = time; m[^(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] an
+d ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13786 seconds
[0] Perl> $c =0; $t = time; m[^(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] an
+d ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13947 seconds
[0] Perl> $c =0; $t = time; m[^(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] an
+d ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.12269 seconds
[0] Perl> $c =0; $t = time; m[^(?=.*a)(?=.*e)(?=.*i)(?=.*o)(?=.*u)] an
+d ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13944 seconds

[0] Perl> $c =0; $t = time; m[(?=^.*a)(?=^.*e)(?=^.*i)(?=^.*o)(?=^.*u)
+] and ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.12400 seconds
[0] Perl> $c =0; $t = time; m[(?=^.*a)(?=^.*e)(?=^.*i)(?=^.*o)(?=^.*u)
+] and ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.14011 seconds
[0] Perl> $c =0; $t = time; m[(?=^.*a)(?=^.*e)(?=^.*i)(?=^.*o)(?=^.*u)
+] and ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13754 seconds
[0] Perl> $c =0; $t = time; m[(?=^.*a)(?=^.*e)(?=^.*i)(?=^.*o)(?=^.*u)
+] and ++$c for @words; 
printf "Found $c matches in %.5f seconds\n", (time()-$t);;
Found 1905 matches in 0.13191 seconds
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