MySQL optimizing buffer_pool_size among buffer_pool_instances - where is the trade off?

Question

I'm looking to optimize MySQL INNODB by tuning buffer pool individual instances.

According to the MySQL documentation:

"The total size you specify is divided among all the buffer pools. For best efficiency, specify a combination of innodb_buffer_pool_instances and innodb_buffer_pool_size so that each buffer pool instance is at least 1 gigabyte."

However, this doesn't specify the optimum approach to defining innodb_buffer_pool_size. Which of these is considered a better approach:

a) a larger number of smaller buffers (given that each buffer instance is >1GB)

e.g. 45 buffers instances over 50GB buffer pool

or

b) a smaller number of larger buffers

e.g 5 buffer instances over 50GB buffer pool

?