If you're using libdispatch on the 4S you might consider using a serial queue (for NSOperationQueue just set the maxConcurrentOperationCount to 1) as it starts to eat the CPU pretty quickly if you're trying to load a lot of images.

Even on the 5 I was surprised by how much it helped to have the images cached (no anecdotal data on the 5S as it came out way after we started caching)