HD space isn't actually a big factor in how fast the game will run.
Your Memory and Graphics Card play the biggest factors.
I'd say for smooth gameplay you want at least 4 GB of DDR2 Memory and I think any old NVIDIA Ge-Force graphics card will do.
:V
I'm not an expert in this field though... so I might be wrong.
8GBs of DDR3 I take it.
If your tower is new then you shouldn't have any issues. You might get a few spikes of low FPS here and there.
You might get some slow down depending on where you live too, seeing as we're connecting to Taiwanese servers.