%#! time luatex  "\count300=10\input test05-speed.tex"
\input luatexja-core.sty

\newcount\cnt\newcount\cnta
\cnt=0\output={\deadcycles=0\setbox2000=\box255}
\long\def\loop#1\repeat{\def\body{#1}\iterate}
\loop\ifnum\cnt<\count300 % <= this value
  \cnta=0 \message{\the\cnt:}\par
  {\loop\ifnum\cnta<500 あ．「い，うえお・か（き）く）（けこ\advance\cnta1\repeat}
  \advance\cnt1
\repeat

\end

%     real time:
% 40: 17.453 14.234 12.98
% 30: 13.254 10.624  9.65
% 20:  8.771  7.097  6.72
% 10:  4.927  4.14   3.81
% env: C2D E7300, Mem 4GB, LuaTeX 0.71.0pre, Gentoo amd64 unstable