Once you hit whatever level gets 60% block, it takes a serious dive in points per 1% added. Like it's virtually useless to put points in it after you hit 60%. I don't have the exact numbers, but effictively aim for 60% max.
at
slvl 2979 you would hit only 69% blockrate (using 999 to sin skills and 999 to shadow diciplines)
same as slvl999 at
slvl500 68%
slvl250 68%
slvl100 66%
slvl 50 64%
slvl 26 60%
when you take into account your +skills from charms and equipment that you will b using 26 is the number that you want to hit imo