The speed is set to a maximum of 256knps on usenet on level 1 management at peak. However as the traffic is restricted it's put in the bronze queue which is the first traffic to get dropped when the network is busy, i.e. at peak times. With the speeds on Usenet and P2P slower than normal (see http://usertools.plus.net/status/archive/1158168848.htm for details) the speeds on leve1 management will be even lower.
I'd recommend scheduling usage off peak as it should run fine then.