If you still have RAM left, this will not affect performance. What is your actual problem?
i facing the problem related to resource like..
LCD is not starting.
DAC is also not working.
UART can receive ISR interrupt.
if i commented the some code of project than its work perfect.
so i realized that the problem is related to RAM or ROM because both cross the 80%.
Maybe you can attach your project. When it compiles fine, it should also work.
Are you using dynamic memory allocation ('malloc')?