The save function allows default values for some arguments to be specified in save.defaults in options. The compression type can be specified, but not the compression level.
This is a problem especially with xz compression, where the default compression level is set to 9, which can be very slow with large files. The range of compression times between the various levels is wide with file sizes even at the lowest levels still being smaller than with gzip. xz at a lower level (e.g. 3) would in some cases be a good compromise between the huge file size of gzip and long compression time of xz=9.
I can provide benchmarks if needed.
Granted in R-devel