I think I misunderstood what you were saying. By "in-memory KVS" with "access times in the microseconds" I thought you were implying a KVS hosted on the server that handles the requests. Otherwise, even if the KVS can respond in 100us to a local query, network latency is going to add much more than that.
Ah ok, that makes sense. Over loopback, you can roundtrip Redis at least as fast as double-digit micros. Intra-DC, your network latency should be somewhere in the triple-digit micros. I'd say if you're not seeing that, something is probably wrong.