You can stream with 1 Mb upload even with 720 p with the right settings, but you don't want to web browse at the same time and stay away from anything using more bandwidth. Basically you can stream with good quality on that low of upload speed if you don't use any other bandwidth lol
For streaming and video capturing you want to have a good amount of RAM, maybe like 6 would be nice, also a good video card IS necessary. Of course you want decent parts for everything else.
Btw when using Xsplit, take the preview down to 10%, then it uses alot less computer power to display the video and makes your computer run alot faster