Re: Which of these VPS configurations would perform better for Cassandra ?

[Radim Kolar]

with 2 GB RAM be prepared to expect crashes because it hardly can handle 
peaks with increased memory consumption by compaction, validation, etc. 
KVM works good only if you are using recent version and virtio drivers 
and provider is not overselling memory. At shared hosting you will not 
be able to handle io loads during peak times and handling peak times is 
most important for any web site.

get 2 old computers in second hand shop, put 6 hard drives to each and 8 
GB RAM, then send these servers to hosting facility.

you are trying to save money at wrong place.