Do you have data for the difference in latency &/or bandwidth between servers on the same rack at Hetzner vs. on different racks?
I was assuming that having the servers in different racks would be an advantage, mainly because the reason I have multiple servers is for data redundancy (I'm using Riak and data is replicated across the cluster.) However, in Riak the servers do talk to each other a fair bit.
The latency and bandwidth between a given server and a web browser out in the world shouldn't vary much from rack to rack, I'm assuming.