It takes time, my 2TB disk plotted 3-4 days as far as i remember. And yes threads and cores are related - each 1 physical core got 2 threads, so it's always threads=cores*2.
I am trying the GPU plotter right now. Its already 3 times faster. but still it says it would take 5 days to plot a 5Tb. And then after that i still need to optimize the plots, so i dont know how long this optimizing will take..?
If i check IMINEBLOCKS on youtube, he doing 25.000 nonces per minute. I am doing with my GPU only 2500 but its already lots faster then my CPU
http://imgur.com/a/VRcps