We are shipping 13.0 and 9 with DSE 3.0 right now.
dse-3.0 $ find . -name "*guava*"
./resources/cassandra/lib/guava-13.0.jar
./resources/dse/lib/guava-13.0.jar
./resources/hive/lib/guava-r09.jar
./resources/mahout/lib/guava-r09.jar
./resources/cassandra/lib/guava-13.0.jar
./resources/dse/lib/guava-13.0.jar
./resources/hive/lib/guava-r09.jar
./resources/mahout/lib/guava-r09.jar

So changing to 8 is just screwy.