If you are doing RAID 10 then I'll prefer getting bigger drives and do a hardware mirror using real hardware RAID card, but it's your choice.
I never really used any software RAID before but I have really bad experience using Intel's on board software RAID, it was terrible, on multiple machines。 It could be out of sync even after a simple reboot and start re-mirroring. It was bad experience many years back though.
Make sure Molex connector is tightly connected, if not, HDDs can lose power easily caused by vibration or moving around the machine, which can cause all sorts of RAID problems.