RAID1 and RAID6 arrays disappeared in Dell PERC6, all disks are listed as available

I had such recovery experience on LSI MegaRAID SAS (which is an OEM for Dell PERC), but in my case nothing was written onto the disks — the RAID10 array was simply mistakenly removed, the mistake immediately recognized and the system shut down. When I re-created the array without initialization, everything appeared to be fine.

What you suggest would be a correct recovery procedure: assemble the same-shaped arrays from the same disks, without initialization. I doubt there is correct foreign metadata, as it must have been overwritten when RAID5 was created. But, knowing that RAID5 might have written something onto disks data area, I would not have much hope that data will appear intact. The background initialization has probably started immediately, so at least a few sectors in the beginning of the disks would be overwritten. That means, some parts of the file system would be damaged beyond repair. Whether it could be recovered or not, depends on how much was damaged.

This is exactly the kind of the situation backups are for: a human mistake. Check if they work if you have them, and in that case, try to recreate RAID6 and then run its consistency check, and try NTFS recovery tools like GDB NTFS on it. It is only reasonable to do if there might be newer data versions than in backups; and, whatever is not recovered that way, you fill from backups.

If you don't have backups, it's still the way to go, but you'd advised to make dumps of your disks first. Needs a lot of spare space and work, right? That's why data recovery services would charge you a lot for this job. Seriously, if the data is valuable and for whatever stupid reason there was no backup, but you are asking this question, don't try to recover yourself. Better ask paid professionals.

As for the system disk, I think it's wiser to just reinstall the OS and software, than to cope with any anomalies it might have gotten even if its file system somehow gets recovered.