But as [B]maineman[/B] says, it’s not necessarily speed of read/write which is affected, but also total capacity.
Any block of whatever size has to have some space within it reserved for disk filing system parameters, as well as data. This reserved space is the same size whether it’s a 64K or a 4K block. It therefore follows that a 64k block has significantly more space for data than the ‘equivalent’ 16 x 4K blocks.
I’d say if the vast majority of what’s being stored is video, and always likely to be so, then you should choose the largest block size possible (yes, even 4096).