# Vertical alignment of \multirow using fraction as subscript

I am using booktabs and multirow to build my table. Below is my sample code,

\usepackage{multirow,booktabs}
\begin{document}
\begin{tabular}{lllllllr}
\toprule
\multirow{2}{*}{$\#$} & \multirow{2}{*}{$f$} & \multirow{2}{*}{$J$} & \multirow{2}{*}{$Re_{\frac{3}{4}}$} & \multicolumn{3}{c}{$w = 8$} \\
\cmidrule{5-7}
& & & & $\Delta t_{x}$ & $\Delta t_{y}$ & $\Delta t_{z}$\\
\midrule
\end{tabular}
\end{document}


and I am getting below table. Notice the Re is little above J and this is due to fraction as subscript. Is it possible to position Re same as J?? You can either smash the fraction, or use \sfrac. I cropped the \cmidrule as it looks nicer (in my opinion):

\documentclass{article}
\usepackage{amsmath}
\usepackage{array, multirow,booktabs}
\usepackage{xfrac}

\begin{document}

\begin{tabular}{*{6}{l}r}
\toprule
\multirow{2}{*}{$\#$} & \multirow{2}{*}{$f$} & \multirow{2}{*}{$J$} & \multirow{2}{*}{$Re_{\smash[b]{\frac{3}{4}}}$} & \multicolumn{3}{c}{$w = 8$} \\
\cmidrule(lr){5-7}
& & & & $\Delta t_{x}$ & $\Delta t_{y}$ & $\Delta t_{z}$\\
\midrule
\end{tabular}
\vskip1cm
\begin{tabular}{*{6}{l}r}
\toprule
\multirow{2}{*}{$\#$} & \multirow{2}{*}{$f$} & \multirow{2}{*}{$J$} & \multirow{2}{*}{$Re_{\sfrac{3}{4}}$} & \multicolumn{3}{c}{$w = 8$} \\
\cmidrule(lr){5-7}
& & & & $\Delta t_{x}$ & $\Delta t_{y}$ & $\Delta t_{z}$\\
\midrule
\end{tabular}

\end{document} 