Physical I/O is your slowest hardware resource. CPU and memory are very fast compared to any actual disk activity even with solid state drives. When you have two physical files responsible for 36% of all physical reads across your entire application and system it might be time for some better data maintenance on these two tables.

How old is the data in these files? Are there decades of closed transactions in these open transaction files? Has data ever been purged or archived? Are they in desperate need of some file reorgs? How well or how poorly are these files indexed? Do you have SQL continuously performing table scans on these files?