How much the sync mount option of the ext3 filesystem slows you down?

Literature says that if you want assured write consistency on your filesystem you should mount it with the sync option.
This way every write is immediately committed to the disk at the cost of a performance hit. But how much?
While working on a broader project I had the chance to test the write performance of sync mounted filesystem vs the same filesystem mounted with full caching and journaling enabled.
The filesystem was on single LUN on an enterprise class storage with 4Gbit/s fibre channel connection to the host.
Throughput was measured looking at the block-out counter of a vmstat 1 command.

Results are:
  30MB/s with sync on
250MB/s with sync off

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