So far, the run-away performance winning configuration for a dataset full of small-ish and not-so-small-ish files.

infinispan.xml

<infinispan xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="urn:infinispan:config:5.2 http://www.infinispan.org/schemas/infinispan-config-5.2.xsd"
            xmlns="urn:infinispan:config:5.2">

  <global>
    <globalJmxStatistics enabled="false" allowDuplicateDomains="true"/>
  </global>

  <default>
    <expiration wakeUpInterval="-1" />
    <unsafe unreliableReturnValues="true" /> 
  </default>


  <namedCache name="FedoraRepository">

    <eviction maxEntries="500"  strategy="LIRS" threadPolicy="PIGGYBACK"/>

    <transaction
        transactionManagerLookupClass="org.infinispan.transaction.lookup.GenericTransactionManagerLookup"
        transactionMode="TRANSACTIONAL" lockingMode="PESSIMISTIC"/>
    <!--
        Define the cache loaders (i.e., cache stores). Passivation is false because we want *all*
        data to be persisted, not just what doesn't fit into memory. Shared is false because there
        are no other caches sharing this file store. We set preload to false for lazy loading;
        may be improved by preloading and configuring eviction.

        We can have multiple cache loaders, which get chained. But we'll define just one.
     -->

    <loaders passivation="false" shared="false" preload="false">
      <leveldbStore xmlns="urn:infinispan:config:leveldb:5.2"
                    fetchPersistentState="true"
                    location="${fcrepo.ispn.repo.CacheDirPath:target}/data"
                    expiredLocation="${fcrepo.ispn.repo.CacheDirPath:target}/expired"
              >
      </leveldbStore>

    </loaders>
  </namedCache>

</infinispan>

repository.json

{
    "name" : "repo",
    "jndiName" : "",
    "workspaces" : {
        "predefined" : ["default"],
        "default" : "default",
        "allowCreation" : true
    },
    "query" : {
        "enabled" : false,
        "indexStorage" : {
            "type" : "filesystem",
            "location" : "${fcrepo.modeshape.index.location:target/indexes}",
            "lockingStrategy" : "native",
            "fileSystemAccessType" : "auto"
        }
    },
    "storage" : {
        "cacheName" : "FedoraRepository",
        "cacheConfiguration" : "${fcrepo.infinispan.cache_configuration:config/infinispan/leveldb/infinispan.xml}",
        "binaryStorage" : {
            "type" : "file",
            "directory" : "/data/tmp/binaries",
            "minimumBinarySizeInBytes" : 4096
        }
    },
    "security" : {
        "anonymous" : {
            "roles" : ["readonly","readwrite","admin"],
            "useOnFailedLogin" : false
        },
        "providers" : [
            { "classname" : "org.fcrepo.http.commons.session.BypassSecurityServletAuthenticationProvider" }
        ]
    },
    "node-types" : ["fedora-node-types.cnd"]
}