I mean it's simple math. If it takes me 1.30 for a full iso on your local machine with a cd rom that's at max capacity (although if I tested it if be willing to bet it's far less than that even using an x64 chipset, my cab is only an x86 with 4GB of RAM) youre taking considerably less for a smaller image.
Mind you not all iso's are maxed, and I have a modest machine so yours may be higher end than mine. If you want my advice, compress a few images and run a benchmark test on the decompression time.
And although I have an image for my controls, the foreground is a 'Please Wait' dialog box with the faux progress bar that GameEx uses when, say, loading databases on startup.