[CentOS] RAID 6 - opinions

I'm setting up this huge RAID 6 box. I've always thought of hot spares,
but I'm reading things that are comparing RAID 5 with a hot spare to RAID
6, implying that the latter doesn't need one. I *certainly* have enough
drives to spare in this RAID box: 42 of 'em, so two questions: should I
assign one or more hot spares, and, if so, how many?

       mark