Unfortunately the guys from Dell are assuming everyone has exactly the same environment. Hopefully you have full control over your configuration and not them!
I would recommend not 2 x RAID10 (which was actually what you described and not 4 😉 ) with but 3x RAID10. The important of separating the three datafile/database types can't be over-estimated! That might start pushing the boundaries of your capacity but I still wonder if the problems you are facing are hardware-based (where you will be spending your money) or configuration-based.
Regardless of what the guys from Dell think (especially when you consider what they 'believe' their hardware can do!) you should follow the advice that your own experience has taught you.