He's right, Grabit wont be the problem for slow downloads. But I did find that Grabit used to take ages to decode and grind the hard drive like crazy. It got so bad that it used to take longer to decode than to download. Just a suggestion, but try using alt.binz http://www.altbinz.com. It's the new kid on the block as far as binary newsreader's are concerned but imo is far superior than Grabit in the way it decodes.
I have Grabit and use usenetserver. Usenetserver has an option to switch servers (has three other servers to choose from) and I did and it doubled my download speed but still hasn't maxed me out yet.