Assuming your disks are the performance bottleneck (such as for random small block IO), you'll be able to better utilize your drives if you have them all in the same raid. Since it's raid 10, your rebuild times won't increase as you scale the raid.
If you split the disks into two raids, you'll be able push the same number of IOs per second over the drives, but only half of the total will be doable on any given volume. If you put all your drives into one raid, each head is used for every IO.
My recommendation is to make one big raid, but make several volumes out of it to ensure you're not hitting any limits on in flight IO or saturating one controller while the other idles.