Choosing the right storage block size for sql server

The method is the one used in the article that you linked in your question: test it. You can capture a representative workload for your application/database and replay that workload on servers that have different cluster sizes. What you will find out is that SQL Sever works best with 64KB clusters, because of the way it reads data from disk (read-ahead).

However, you don't have to do that: setting a 64KB cluster size is an established best practice, as clearly stated in the article that you refer to. From the article:

The file allocation unit size (cluster size) recommended for SQL Server is 64 KB; this is reflected in Figure 4.

If you decided to test the performance under different cluster sizes, you would probably discover that the difference is negligible, especially on high-end storage systems.

The 64K block size comes from the fact that SQL Server does its I/O in units called "Extents", which are each 8 pages - and a page is 8K so the basic unit of I/O is 8 X 8K = 64K.

Paul Randal explains here.