In my configuration there is :
Memory Soft Limit (bytes) 512M
Memory Hard Limit (bytes) 768M
Because eaccelerator memory is set to 256M.
I have no script which consume more than 300M (php script + eaccelerator shared memory)
I understand you can't correct all the specific problem of the users... This configuration work fine with phpFcgi, I will let the script handler to it and I check if it work with phpLsapi in future release.