Client Side it is the maxBufferSize on the transport element in your DataCacheClient config section.
<transportProperties ..whatever else you have.. maxBufferSize="8388608" />
Edit:
Example of the DataCacheClient section from MSDN
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<!--configSections must be the FIRST element -->
<configSections>
<!-- required to read the <dataCacheClient> element -->
<section name="dataCacheClient"
type="Microsoft.ApplicationServer.Caching.DataCacheClientSection,
Microsoft.ApplicationServer.Caching.Core, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=31bf3856ad364e35"
allowLocation="true"
allowDefinition="Everywhere"/>
</configSections>
<dataCacheClient requestTimeout="15000" channelOpenTimeout="3000" maxConnectionsToServer="1">
<localCache isEnabled="true" sync="TimeoutBased" ttlValue="300" objectCount="10000"/>
<clientNotification pollInterval="300" maxQueueLength="10000"/>
<hosts>
<host name="CacheServer1" cachePort="22233"/>
<host name="CacheServer2" cachePort="22233"/>
</hosts>
<securityProperties mode="Transport" protectionLevel="EncryptAndSign" />
<transportProperties connectionBufferSize="131072" maxBufferPoolSize="268435456"
maxBufferSize="8388608" maxOutputDelay="2" channelInitializationTimeout="60000"
receiveTimeout="600000"/>
</dataCacheClient>
</configuration>