'Terrible performance' is in the eye of the beholder. So is reliability. Software RAID is constrained by bus bandwidth, so RAID 10 writes may well be slower than RAID 5 if you're bus-limited: and even RAID 5 writes are no slower than writes to a single drive. TBH, 89Mb/s writes and 250MB/s reads (which my Areca card can manage with a four-drive RAID 5 array) don't seem too 'terrible' to me.
Furthermore, reliability is fine *if* you can be sure that once RAID parity computations have happened the stripe will always hit the disk, even if there is a power failure. With battery-backed RAID, this is going to be true (modulo RAID controller card failure or a failure of the drive you're writing to). Obviously if the array is sufficiently degraded reliability isn't going to be good anymore, but doesn't everyone know that?