Data Size on each node

[Sachin Nikam]

We currently have a Cassandra Cluster spread over 2 DC. The data size on
each node of the cluster is 1.2TB with spinning disk. Minor and Major
compactions are slowing down our Read queries. It has been suggested that
replacing Spinning disks with SSD might help. Has anybody done something
similar? If so what has been the results?
Also if we go with SSD, how big can each node get for commercially
available SSDs?
Regards
Sachin