Document when zio-kafka is faster than raw java kafka (#1403)

docs/index.md

@@ -4,7 +4,9 @@ title: "Getting Started with ZIO Kafka"
 sidebar_label: "Getting Started"
 ---
 
-[ZIO Kafka](https://github.com/zio/zio-kafka) is a Kafka client for ZIO. It provides a purely functional, streams-based interface to the Kafka client and integrates effortlessly with ZIO and ZIO Streams.
+[ZIO Kafka](https://github.com/zio/zio-kafka) is a Kafka client for ZIO. It provides a purely functional, streams-based interface to the Kafka
+client and integrates effortlessly with ZIO and ZIO Streams. Often zio-kafka programs have a _higher_ throughput than
+programs that use the Java Kafka client directly (see section [Performance](#performance) below).
 
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@@ -135,3 +137,14 @@ Want to see your company here? [Submit a PR](https://github.com/zio/zio-kafka/ed
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 * [Rocker](https://rocker.com)
 
+## Performance
+
+By default, zio-kafka programs process partitions in parallel. The default java-kafka client does not provide parallel
+processing. Of course, there is some overhead in buffering records and distributing them to the fibers that need them.
+On 2024-11-23, we estimated that zio-kafka consumes faster than the java-kafka client when processing takes more than
+~1.2ms per 1000 records. The precise time depends on many factors. Please
+see [this article](https://day-to-day-stuff.blogspot.com/2024/12/zio-kafka-faster-than-java-kafka.html) for more
+details.
+
+If you do not care for the convenient ZStream based API that zio-kafka brings, and latency is of absolute importance,
+using the java based Kafka client directly is still the better choice.