(Ozgun from Citus Data here.)
We're going to publish more comprehensive results in a few weeks. In our initial tests, we found the speed up to depend a lot on the underlying data and the type of queries.
For example, we found that when compression reduced the working set from being on disk to in-memory, there was a significant jump.
Also, we're looking to do optimizations on the cost estimation side -- these will notably help with queries that join multiple tables together, a common scenario for the TPC-H benchmark.