Your laptop was likely Wireless G. This is an Wireless N card, which is compataboe with 2.4 GHz G and can operate in that range, but generally will attempt to operate in Wireless N mode (5 GHz) if your router supports it. If your router dowsn't yet support wireless N, that would be the first fix I would try. Even if that isn't it, you still would have an updated router out of it.
Next thing to try would be to see if you can tie those random severe latancy issues to ioeration of another electronic device in the general area of your computer. Does it only happen when someone is on the phone? or when your cell phone is docked near your router? Does it only happen when someone uses the microwave, or operates a garage door opener nearby, etc.
If you can't tie it to a specific event, see if your computer is having any issues in Event Log around the same time. Also try switching from the Asus provided wifi software to the windows native software and see if that helps.
If all that doesn't do the trick, then you start looking at the advanced class troubleshooting steps. Download and install Wireshark http://wireshark.com/
then run it in the background, with your wireless network card selected as the source to monitor. Once you have it enabled when one of the random latancy issues occur, stop the log and take a look at the log file for any red and black line items. If you need help interperting the log, I can assist, but please be aware the log file will contain private information in various forms, including possibly passwords and account information you type in while logging, so you'll want to sanatize that part before you send anything.
Asus usually makes decent wifi cards. I suppose it could possibly be the chipset driver too. Maybe check for an update for your motherboard drivers. Are there any unknown devices in device manager, or errors in event log?