Maximum allocated blocksize depends on your DASD devices, disk geometry and your record length. The allocation is based on CKD devices. Most modern DASD (Fixed Block Architecture) emulates CKD models. For optimum allocation, try coding BLKSIZE=0 in the DCB when creating your dataset (the system will define the block size for you).
Using BLKSIZE=32760 on a 3390-3 DASD may create a mucho wasted space, since it is not a whole multiple of track size. Try to allocate block size that is when multiplied (factored), it is as close to the Track Size (56,664) as possible.
For BLKZISE=32760, unallocated space per track = (56,664 - 32,760) = 23,904 bytes