You’ll be fine. You have three disk redundancy. If one of the disks fail you’ll still have two disk redundancy during rebuild. You could lose 2 more drives during rebuild and still have all your data. What is the likelyhood of three disks failing during rebuild?
The likelyhoods are calculated with multiplication. If the likelyhood of one disk failing during rebuild is 0.01 then the likelyhood of two disks failing is 0.01 * 0.01 = 0.0001. Three disk failure would be 0.01 * 0.01 * 0.01 = 0.000001. One out of a million.
It’s way more likely to ruin the files by accidental deletion, destructive commands, software errors, massive hardware failure like your power supply failing and destroying all your drives at the same time or your house burning down.
Aren’t any modern HDDs faster? Even 5400 rpm HDDs because when capacity grows one rotation of the disk will contain more data.