Your point is technically valid but irrelevant in practice. The compressed tar is surprisingly small and you can stream it to S3 if you really want to shave off

Your point is technically valid but irrelevant in practice. The compressed tar is surprisingly small and you can stream it to S3 if you really want to shave off megabytes. But more importantly, you don't care. This will give you 3 orders of magnitude better write throughput with 2 hours of work. The savings in engineering time alone will buy you 1000x the ram you wasted! With that kind of achievement, my advice would be leave over-optimization for later and buy yourself a drink :)