MongoDB 3.0, featuring the optional WiredTiger storage engine, was benchmarked against Couchbase Server by Avalon Consulting to assess performance improvements. While MongoDB claims WiredTiger offers significantly faster write performance than the default MMAP storage engine, the benchmark revealed that Couchbase Server outperformed MongoDB, particularly in terms of throughput, with Couchbase maintaining lower latency under higher client loads. The benchmark, conducted on Amazon Web Services using the Yahoo! Cloud Serving Benchmark, demonstrated that Couchbase Server could handle more concurrent clients while keeping latency under 5ms, a threshold MongoDB exceeded with fewer clients. The test highlighted that MongoDB's limitations were more related to sharding than the storage engine itself, suggesting that MongoDB would require significantly more nodes to match Couchbase's performance, pointing to concurrency constraints as a limiting factor in MongoDB's architecture.