Hey Martin,
Same thing here! Today spend a whole day on fine tuning my website custom IT.
I went from a google page speed score of 58% for desktop to 80% after tuning everything. Especially the Minify option was great.
--BUT--
One thing remaining is the "Image Compression". Sad that this function isn't being fixed by the W3TC plugin. I suggest we should fined another plugin? Although is it rly worth saving a couple of kB's?