Some Block Producers, such as HelloEOS and Bitfinex, are already testing EOS VM on the EOS Mainnet. According to the results shown on AlohaEOS' tools, we can already witness a CPU improvement of more than 5 times.
In fact, taking Bitfinex as an example, the execution time of their node has gone from about 1.30ms to about 0.23ms, resulting in a reduction in execution time of over 80%.
We can evaluate as well how the performance has improved since the launch of the mainnet. Again using AlohaEOS' tool, we can observed that in August 2018 the Block Producers' execution time was around 12ms. As a result, using EOS VM we are having an improvement of more than 50 times compared to the first months of EOS, with a reduction in execution time of about 98%.