Well assuming you're able to reach the speeds your line sync is set at
a 192 line will get 256kbps or 32kB/s (80% of 320kbps)
a 384 line will get 410kbps or 51kB/s (80% of 512kbps)
a 512 line will get 512kbps or 64kB/s (80% of 640kbps)
I went for 384 as it's almost twice the speed of 192 and not too far off 512 speeds
This may just be my opinion but what a waste of money and a waste of the ability to provide that speed.
I mean, with port shaping and that little excuse for a cap how could you really justify the extra money just for a couple of seconds or minutes extra speed, obviously depending on the file size you download.
But since the little cap is there, utilizing this extra speed inorder to download a large enough file that makes a difference time wise would mean that it wont be to long till you get capped.