Hi
The larger size of buffersize, the better but it is dependent on your RAM. And also you may increased the size your paging memory (virtual memory) at OS level then perform rebooting. But I suggest you that start at 800000 (abap/buffersize) and increase the size of your paging memory.
Hi
The recommended size of abap/buffersize for those systems using various modules, running 1 or more app servers and using a lot of custom programs is 800000.