What is the best cluster size for a ReadyBoost ntfs memory card?

How does a cluster size affect the readyboost function? The default cluster size is 2^12 bytes. What about higher order? I think of 2^13 bytes or 2^14 bytes? What is better ExFat or NTFS for ReadyBoost?

Larger cluster size will be better, but will mean more wasted space. It might also help to have the driver formatted as ExFAT.

A larger cluster size means that more data can me read/written from the drive at the same time, increasing speed.

I started testing cluster size and I found that for my 8Gb thumb drive the best format was Exfat at 4096Kb. I tested with DiskMark. Speedgain at 8192Kb was negligible but there was gain over 2048Kb cluster size.

Sequential Read (Q= 32,T= 1) : 19.295 MB/s Sequential Write (Q= 32,T= 1) : 7.864 MB/s Random Read 4KiB (Q= 32,T= 1) : 5.673 MB/s [ 1385.0 IOPS] Random Write 4KiB (Q= 32,T= 1) : 0.015 MB/s [ 3.7 IOPS] Sequential Read (T= 1) : 19.084 MB/s Sequential Write (T= 1) : 7.968 MB/s Random Read 4KiB (Q= 1,T= 1) : 5.321 MB/s [ 1299.1 IOPS] Random Write 4KiB (Q= 1,T= 1) : 0.010 MB/s