I cannot found the maximum number of cluster that a vCenter can manage, only the maximum number of hosts per cluster, that is 32... but absolutely you can have more than one cluster without problem.
Make some math, since vCenter supports 1000 hosts and each cluster can have 32 hosts, maybe the you can have at least 32 clusters... but not 100% about this.
http://www.vmware.com/pdf/vsphere5/r51/vsphere-51-configuration-maximums.pdf
I cannot found the maximum number of cluster that a vCenter can manage, only the maximum number of hosts per cluster, that is 32... but absolutely you can have more than one cluster without problem.
Make some math, since vCenter supports 1000 hosts and each cluster can have 32 hosts, maybe the you can have at least 32 clusters... but not 100% about this.
http://www.vmware.com/pdf/vsphere5/r51/vsphere-51-configuration-maximums.pdf
Assuming you have the necessary resources to run your existing cluster on 6 hosts rather than 8, it should be no problem to vacate two hosts and use them in a new cluster.
We are currently running eleven hosts organized into three clusters on a single vCenter server.