Actually here you go:

I took the first image from here: http://www.dwellable.com/h/8559/Cape-Cod/Upper-Cape-Cod/Falm...

Cropped it to 1024x1024 (you'd of course make a sprite sheet instead). Then shrank it to 512x512 just for demonstration purposes.

I then converted it using texturetool, also back-converting it to make a png with exactly the pixels produced in the PVRTC image:

    $ texturetool -e PVRTC --channel-weighting-perceptual --bits-per-pixel-2 -p converted2.png -o converted2.pvrtc original.png
    $ texturetool -e PVRTC --channel-weighting-perceptual --bits-per-pixel-4 -p converted4.png -o converted4.pvrtc original.png

The PVRTC images are significantly smaller, both on disk and in memory:

    $ ls -l original.png 
    -rw-r--r--  1 kstenerud  staff  571225 Jul 27 15:10 original.png
    $ ls -l converted*.pvrtc
    -rw-r--r--  1 kstenerud  staff   65536 Jul 27 15:12 converted2.pvrtc
    -rw-r--r--  1 kstenerud  staff  131072 Jul 27 15:12 converted4.pvrtc

Here's the quality:

Original image: http://i.imgur.com/flT7c.png

4bpp image (converted back to png): http://i.imgur.com/Itz4F.png

2bpp image (converted back to png): http://i.imgur.com/tzqlw.png