I haven't had any issues with the WiFi signal on the S3. Are you having problems with the One X+ where you cannot surf or send/receive email? Just because the signal drops, it does not necessarily mean that it is an issue. If you cannot surf or sent/receive messages, then I would say it is an issue.
I use to use an HTC Desire Z. Even though I do notice the number of bars on the WiFi indicator drop, I am still able to get a good enough signal to surf and send/receive messages. This happens when I am in a part of the house that is far away from my router. I never did a measurement on it.