Well, your test was an interesting run, but it didn’t take into consideration the “virtualization” differences between the two server types and how they each interact with multiple client server instances.
KVM systems promise to deliver to the client instance a specific amount of memory and CPU resources as well as disk space. The OpenVZ systems “appear” to promise the same things, however in reality they are far more prone to host client loading conditions than the KVM systems.
For example, if you are running an ERPNext system on an OpeinVZ host service and everything is going well, you may be lured into a false sense of a good service level. However, if that hosting company also sells another client an instance on the same hardware that your ERPNext system is host on, you will start to notice some delays in how your system works. In an OpenVZ environment, there is very little in the way of throttling controls to suppress any single virtual server from eating up all of the system resources available on the hardware. So, of the other unknown client server instance sharing your same hardware suddenly starts some complex database crunching your ERPNext instance could come to a complete halt. I have actually experienced this and it is not pleasant. Likewise, if you started some large report in ERPNext that required maybe a year of data to be cataloged, you could potentially shut down someones website being hosted on the same hardware.
KVM systems prevent much of this kind of abuse. They sequester a fixed amount of minimum resources to each virtualized server on the the same hardware. While it is still possible to experience some slow responses on KVM servers, it is usually never a case of being completely immobilized.
Both systems allocate the hardware resources to the highest demand instances, but only KVM systems will assure you of at least having some level of functionality even during times of highest demand on the hardware.
OpenVZ virtualization has improved some over the past 3 years but it is still not the best choice if you are leasing the virtualization services from a VPS provider.
The OpenVZ vs KVM debate is not the only factor to consider when looking at performance. Sometimes it is a matter of the distance to the server that can make or break a performance benchmark. There are actually far too many parameters that directly affect performance to even begin to compare them here.
Do some more research on the pro’s and con’s of the virtualization methods as well as the other factors that directly affect performance before you jump all in on any given providers promises.
Hope this helps, and as always… Your mileage may vary