[plt-scheme] r6rs vs module language performance

Hi,
I ported to r6rs a small research prototype I wrote a couple of years
ago (in mzscheme v.3, I think), to "try and feel" the new standard.
Just to waste some time, I tried on the same input file both the "pure
mzscheme" and the r6rs versions: the former took 5.8s on my machine,
while the latter 1m14s. The application core resides in a single r6rs
library, installed (and compiled) through plt-r6rs --install.

I was wondering if there are performance tips to improve r6rs code in
mzscheme, and what are the main differences between running r6rs vs
module code (just some general ideas, I'm curious).

Thanks for all your nice work,
Matteo