In general the system requirements for Aion are greater than those for WoW. If your issue in WoW is primarily video lag (i.e. your system has a hard time keeping up with all the stuff going on around you) Aion may be a bit too taxing for your machine. If on the other hand your issue has to do with network latency (maybe you see people walk in a jerky or twitchy kind of way or you experience long delays between when you issue a command and things happening) then your problem has to do with your ISP and connection to the game server rather than your system.
I will say on the issue of latency, Aion handles itself worse than other MMOs on average that I've played..
Within the last 4 years or so I've played 3 MMOs seriously.. FFXI, WoW, and now Aion. Here's a breakdown of network responsiveness and the way the game handles it:
FFXI: Servers are located in Japan, game plays with relatively little lag unless you're in an extremely dense area (lots of PCs and NPCs in one place). In this case the game compensates by not rendering (or tracking) some of the characters and their models.
WoW: Servers are located all over the place, some lag in densely-populated areas but the game doesn't seem to care all that much and only really tries to compensate for it if it gets out of hand or the server receives bad data from the client
Aion: US servers are all on the east coast, lag spikes abound and the game responds rigidly by rubber-banding your character back to where the server thinks you're supposed to be. Does not compensate for network latency at all, will not respond to commands after the first one during a lag spike.
All in all, Aion handles lag very poorly when compared to a couple older MMOs (I believe FFXI is 8 years old at this point and WoW is 5 years old).