Finally the last of my testing. I tried an i5 running at a similar speed as the i3 and as expected no difference. A higher speed and overclocked i7K may make a slight difference, but seriously, once any SSD is installed, it comes down more to the number of peripherals (HDD's, SSD's , CDROM, USB devices) installed as this affects BIOS Initialisation time and Windows (drivers) load time. In my system, OS load time is really fast and still less than 50% of BIOS initialisation time.
IMHO once you get sub 15 second times from power on to a working Desktop then it's quick enough for me not to bother using sleep state anymore. Only time will tell if WIN8 maintains these times or if it goes like the others before it and needs refreshing/reinstalling every year or so. Don't have to do that in the CAR-PC as software is not being constantly changed, removed or installed like desktop PC use.
Would I upgrade the CAR-PC? Not right now, but I'm tempted.