How to list content from a tar file without recursion

tar -C changes directory

tar -C /home/user1/ -cvzf dir1.tar.gz dir1

btw, handy one for keeping track of changing directories... use pushd and popd.

pushd .
cd /home/user1
tar cvfz dir1.tar.gz
popd

When you say you want to take advantage of multiple cores the implication is that your tar with gzip is CPU bound and not IO bound, are you sure this is the case? If you are not sure you need to run sar, iostat, top, or check monitoring graphs etc to find out. Never a good idea to try to solve a problem with out understanding it first. Not saying this is the case with you for sure, but my guess would be that even though there is compression with gzip you would be more likely to be IO bound.

If it is IO bound, and you have multiple arrays, a separate process for each array might make sense.

I also second David's advice to consider incremental.