There are a number of scripts/programs out now which combine multiple png optimisation tools in an attempt to get the best result. For example:
pngSlim: http://people.bath.ac.uk/ea2aced/tech/png/pngslim.zip
scriptPNG: http://www.css-ig.net/scriptpng-08-11-2009.zip
Article about performance on various tools here:
http://www.css-ig.net/png-optimisation-compression
It is in French but luckily they use Hindu-Arabic numerals, so the numbers can speak for themselves. 
I appreciate you looked at optipng before and rejected it through too much overhead (Pagetest / Feature Requests / #9 Add OptiPNG to image compression check).
However would it be possible to have an option allowing for the optimisation of gifs → pngs, the crushing of pngs & the palette reduction of png32 → png8 should it be so desired?
I already do palette reduction in the optimization checks and it’s “on the list” to do gif->png as part of the check as well. Are you looking for it to just be checked or do you need the resulting images?
At least up until now, pagetest tells you how much smaller or faster things could be with the optimization checks but it doesn’t package up the resources for you (smushit would probably be a better choice for the actual images to use on your production site).
Thanks,
-Pat
I appreciate that you already do a palette reduction to png8 and jpg quality reduction to 50%. 
Cool to hear that gif->png is in the pipeline as well. BTW is there an online version of the todo list…I had been looking at the feature-request list for pagetest…which might not be the right place.
I had been thinking along the lines of showing even greater savings are possible (with png there are optimisations that can be done to the image after the palette has been reduced) and not along the lines of providing a service for download of optimised images. As you say there is smushit, punypng and others out there who provide that service already. Or we could simply run the tools ourselves. It maybe that the time overhead for running the combined image optimisation tools is too large for an online report.
The feature request list is the official to-do list. I try to put everything in there but sometimes I forget and they’re just in the back of my head There are 2 feature lists, one for pagetest and one for webpagetest.
Running the combined image optimization tools (pngcrush, etc) is what I had looked at but it took too long and was too resource intensive for me to do with every test.
Thanks,
-Pat