Does this describe the situation?

_____    _____________          _______________           __________
|PHP|----|Perl script|--------->| Perl "Clent"|           |        |
-----    -------------           |             |           |        |
_____    _____________           |             |           |        |
|PHP|----|Perl script|--------->|             |           |        |
-----    -------------           |              |------->|Remote  |
_____    _____________           |             |           |server  |
|PHP|----|Perl script|--------->|             |           |        |
-----    -------------           |             |           |        |
_____    _____________           |             |           |        |
|PHP|----|Perl script|--------->|             |           |        |
-----    -------------            ---------------           ----------
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Four (to 10) PHP servers, call a perl script (50X/sec) to send something to a Perl "client" that then forwards those messages to a remote server.

The perl "client" receives boolean responses from the remote server. Does it return those responses to the PHP servers?

The Perl "client" is there to prevent the perl script from having to reestablish a connection to the remote server every time. But having the perl script talk to the perl "Client" via socket would just move the problem back a stage, so your hoping that they can communicate via shared memory. The perl script is involved because you don't know if you can do socket communications directly from PHP.

I find it unlikely that starting a new process and establishing a connection to the shared memory will be any faster than (say) connection to a server socket within the perl "client".