I've noticed that iOS 7 is a lot more aggressive about keeping Wifi turned on than iOS 6 was.
With 6, I'd often unlock my phone and it would take a moment to get back on Wifi. With 7, it's almost always already on Wifi when I wake the screen, even before I unlock. Also, at work where I often get kicked randomly off the Wifi, it rejoins a lot more quickly than iOS 6 did. We're talking a fraction of a second most of the time.
So this many not answer your question directly, but I have noticed iOS 7 being a lot better with Wifi. As always YMMV.