One thing I do to save bandwidth on my bog is make tiny images. But what's important is number of packets, not bytes. I just measured in a packet sniffer. For an MTU of 1500 bytes the first HTTP response packet contains roughly 1130 bytes of image data. Every other packet contains 1460 bytes.
Being conservative, optimal sizes for small images are 1100, 2560, 4020, and 5480. 3000 is no better than 4020.