Personally, if I were using RAID of any sort at all, it would be for the purpose of safeguarding my data, not for performance, otherwise I'd stripe the drives or go RAID 5 with a more upspec controller - something that the current software RAID cannot do. Even if software RAID could do RAID 5 I doubt very much that it can match the performance of a dedicated RAID 5 controller. It is simpler to manage failed drives, reimaging, etc. using a hardware controller than software as well.
Kelvin