Firstly I have approximately 100mbit download / 40mbit upload (http://www.speedtest.net/result/3084662225.png).
I'm having issues trying to maintain decent bandwidth to twitch's servers (Asia: Singapore gateway). Bandwidth tests in xSplit only check in at 1500kbps for my stream. Is there any reason why I should be having these issues?? Is there anything I can do to improve things?
You might try some other servers. A speedtest to a server (potentially hosted within the same datacenter) might be significantly off of real-world sustained testing. Try a test to europe, you'll likely see dramatic drops in speed.