Why I recommend fewer faster arrays (raid10) over higher number of slower arrays (raid1)? Because you might again win some performance. Let me put it this way:
If you have 2 VMs, each of them having its own raid1, what each VM gets is read/write speed roughly equal to that of sigle disk (simplified).
If you have 2 VMs sharing one common raid10, they get about half r/w raid speed (that is the same as above) if they access raid10 concurrently. But if only one VM is in particular moment accessing raid10 array, it gets full r/w speed (which in case of 4disk raid10 is let's say roughly twice the speed of single disk).
It is good to spread load. But if you over-partition your resources, you are loosing flexibility. You can never add them together and re-distribute it according to actual conditions...