Use qr to cache your independent regex's.

my $pattern1 = qr{abc:\(?.*?\)?\s};
my $pattern2 = qr{${variable}.{0,5}\s};

if ($str =~ /$pattern1(.*?)$pattern2/) {
    print "matched $1";
}
if ($str =~ /$pattern2(.*?)$pattern1/) {
    print "matched $1";
}
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Then the length of the regexs won't be an issue.