build a custom PC unless you very VERY stupid. i made my PC when i was 12. with costume computers you can build a PC that runs games as good as another that may cost double the price.
get an i7 CPU (for rendering video) and good Graphic card that you've researched that's -$300, get a $50 power supply (cheaper ones will set your computer on fire) and spend what you think is right on everything else. get either a 1 terabyte hard-drive or a 1 terabyte hard-drive and an external hard-drive which will give you less lag when recording. with my one 1 terrabyte hard-drive i lose around 5+ FPS. try and get at least 8 GB of ram if not more.
i have 16 GB of ram, an i5 3570k, and asus GTX 660 ti and a 1 terabyte hard-drive. for my YouTube(
http://www.youtube.com/user/SirHugington) i use shaders on fancy and far render distance at 60 FPS.
side note: i have an 1080p monitor like most but it only goes up to 60 hertz (normal amount). if your monitor is 60 hertz like most no matter how many more fps your computer says your getting the monitor will only show 60 Frames per second.
Hope i helped out
if you have anymore questions please ask.