Intel X48/P45 RAID 10 question

I implemented two different RAID levels on a Dell Pentium D using 4 SATA II drives and an earlier Intel Matrix RAID controller than you have. I create 1 RAID 0 stripped set across all 4 drives (this held the OS and applications) and a second RAID 10 (or 1+0) stripped and mirrored set across the same 4 drives. Yes, RAID 0 was lightning fast, RAID 10 was faster than a single drive and redundant, and yes, each matrixed RAID appeared as a single drive (i.e. C: and D. When the RAID controller hiccupped and thought one of the RAID 10 drives had gone bad, I was able to successfully rebuild the data on the RAID 10 D: drive. However, when I replaced the physical harddisk that the Matrix RAID controller said was going bad, Intel Matrix RAID controller would NOT let me recreate that first RAID 0 set (i.e. C so I couldn't reinstall the OS and couldn't get at the RAID 10 D: drive, even though Matrix RAID still saw D: and was ready to rebuild it (since 1 drive had been replaced). Bottom line: I don't think the earlier Matrix RAID was ready for multiple RAID levels; the new P45 chip may be, but I don't know. If I were going to rebuild that system, I'd probably create one 4 disk RAID 10 set, then divide it into 2 partitions with 25-30% of the space for my C: (holding OS and apps) and the remaining 70-75% for my D: drive holding my data. Then I'd get an add-in PCI or PCIe SATA card with an external eSATA connection, an external eSATA enclosure and an SATA II drive equal to the drive capacity of the RAID 10. Then I’d set Windows to do automatic nightly backups to the external eSATA drive, because something will go wrong eventually; as others have recommended, and losing data is hell.