12.5% overhead isn't that much. It's what just the networking gear can easily eat in a data center (12% out of all the non-cooling-related power supply).

Reed-Solomon encoding adds 50%, of you want 3 block per 2 data blocks. Replicated encoding (not relevant here since this is allow throughput usecase, but necessary if you want to sustain high read throughput) is adding at least 200% (if you want a 3x replication, which I think should be the minimum).