I've run into the same problem several times w/ my Linksys. The most recent was when trying to stay connected to PSN w/ my PS3.

Honestly, neither of those encryption methods will cause an impact that you'll notice. the overhead is a few hundred K max and wireless has a bandwidth of 54Mb which I'm sure exceeds your home connection.

My suggestion: update the firmware. Every time I've had that issue, I discover a new version came out within the past few months and it always has resolved the problem