Bandwidth (or throughput) is not necessarily the only consideration to take into account. Latency due to buffering and distance are critical to performance on the WAN. You can have a big fat wide pipe, but if your client is in Mumbai and your server is in Chicago, you will still have to cross a big ocean and all of the devices between the client and the server. Some things can be tweaked to get better performance but those things play with the TCP/IP stack and may not be compatible with all applications or uses.
There are lots of bandwidth calculators out there like http://web.forret.com/tools/bandwidth.asp.
Looks like you want someone to write this paper for you ;).