For 100% read workloads, the impact to maximum throughput can be significant. That's a pretty uncommon workload for us though. It's likely a single-digit percentage problem at 50% reads.
Two nice things about VoltDB users: 1) They often are very write heavy, 99% read-write transactions isn't uncommon. 2) Few are using anywhere near the maximum throughput for their machines. Most size their clusters for appropriate storage and redundancy, not throughput.
The lost write issues weren't optimizations, just implementation bugs. Sigh.