Rotating the primary shard in /solr/select

[Phillip Farber]

Is there any value in a round-robin scheme to cycle through the Solr 
instances supporting a multi-shard index over several machines when 
sending queries or is it better to just pick one instance and stick with 
it.  I'm assuming all machines in the cluster have the same hardware specs.

So scenario A (round-robin):

query 1: /solr-shard-1/select?q=dog... shards=shard-1,shard2
query 2: /solr-shard-2/select?q=dog... shards=shard-1,shard2
query 3: /solr-shard-1/select?q=dog... shards=shard-1,shard2
etc.

or or scenario B (fixed):

query 1: /solr-shard-1/select?q=dog... shards=shard-1,shard2
query 2: /solr-shard-1/select?q=dog... shards=shard-1,shard2
query 3: /solr-shard-1/select?q=dog... shards=shard-1,shard2
etc.

Is there evidence that distributing the overhead of result merging over 
more machines (A) gives a performance boost?

Thanks,

Phil