performance issue with PEAR:HTTP

I am using the PEAR SOAP package to implement a webservice on top of an exsiting set of PHP scripts. Mostly, it consists of building a SOAP envelop containing a collections of arrays (filename, filesize, filecontent - base64 encoded) and sending it to the web service. When the request is small [5mb], the transfer time is around 20 secs. When the request becomes big [60mb], transfer time goes to the roof.. >> 350 secs Trying to understand why, I used some logging (thanks log4php) and the debug/profiling extension xDebug. I narrowed down the bottleneck to the actual HTTP:sendRequest method which specifically takes most of the time, ie. the fputs() takes forever to complete. I compared on the same hardware with a simple POST of the same file via an HTML Form, and the transfer time is 1 sec. No comparison. So I wonder where is such a difference comes from ? Is there anything obvious I missed ? Is there a workaround or some improvement that can be made ? Thanks for any help. Romain.