Changing page-cluster from 5 to any lower value may cause some problems - it is assumed that eMMC cluster size is 128KB (page-cluster=5). That means eMMC chip writes only by 128KB blocks. So, if you write less than 128KB it may READ 128KB "sector", then replace some portion of it and write 128KB ---> slower speed and flash wear increase.

However, I am saying "may" because if eMMC chip is smart enough it can combine the multiple short sequential writes to a single 128KB in some buffer. Unfortunately, I don't know the specs of eMMC chip.