>How is this combination going to work in terms of performance?
>I am afraid that sending simultaneous request will slow down the response time.

You should not have an issue with performance if you use multi-threaded DLLs. I regularly test VFP COM DLLs by simulating 40 clients pounding the server for days at a time, generating as many as 3 million hits per day (on a four-proc machine with 2Gb of RAM and striped RAID). If you're site is generating more hits per day than that, I think other stuff is going to break down before your COM servers. :-)