I want to change the font size of the table using print.xtable.
Using
print(xT, size="\\tiny")
works but I don't know other options for size. Something like size="7pt" would be nice.
You may choose a particular font size with the \fontsize{<size>}{<line space>}
command:
print(xt, size="\\fontsize{9pt}{10pt}\\selectfont")