Maybe you intended to say that you have WR1043ND? There is no model 1024nd on TP-Link's site.
Anyway, I have WR1043ND, and use both nzbget and nzbgetweb. This combination works works very well, and while nzbget uses a lot of RAM, it almost doesn't use CPU (usage is 4-5%) and downloads max out my connection speeds ( ~320Kb/s).
The reason why you get different result may be related to a configuration. In the beginning I also had severe performance issues, but some tweaking resolved them.
It is very important to change value of WriteBufferSize. By default it is set to 0. As the result, I/O is very high - on my router I/O usage was constantly above 90%, which caused both significant drop in download speed (which reached 100Kb/s at it's peaks) and overloaded the machine so that it barely responded. After I changed buffer size to 2Mb I/O dropped to 6-8%, machine became responsive and download speeds reached maximum levels. BTW, setting buffer size to -1 will probably be even a better idea, since automatic cache management may use RAM more efficiently, but I am pleased enough with the current results.
In addition, related to your earlier posts: I just unset doc_root, otherwise it seems that if you install additional web server components which use PHP they may not work properly, since setting doc_root to a particular directory will prevent serving files outside this directory (see PHP documentation for doc_root). Also, I installed php5-mod-json instead of json_rpc (there is no such package in openwrt repository for the device).