Hardware Requirements For Many Connections

I have decided to stick with a product that has real support instead of "open source." I have a simple question:

What are the hardware requirements to provide 100-250 concurrent connections at, say, 300kbs? I have customers that want that many. Would I basically need a dedicated server per customer, or can a robust server handle 1000+ concurrent connections? Is a CDN a better solution? I've noted a minimum of XEON 3.2 and 4GB of RAM but recognize that is a minimum. I generally prefer dual Opteron's with RAID 0 for speed and fast drives. How about quad-core Intel's? Is there really a difference anymore between XEON with a 1MB L2 cache and a dual core with 1MB of L2?

Thanks in advance.