50MB/sec is likely from a very loaded RAID array shared amongst many VPS users, using older disk technology. They are likely overselling and over-provisioning users to get as many accounts on a single server as possible. Most providers nowadays are using SSDs unless you need a LOT of online storage, which then makes more sense to use "spinning rust." But then again, I'm running my own servers at a colocation facility, so I have RAID SSDs and backup HDs tuned to my configuration needs! So I/O blocking is not so much an issue for me.