Sorry
System Information probably uses the phrase 'Boot ROM Version' to show the firmware for that iMac
EFI and SMC firmware updates for Intel-based Macs
I guess that for Yosemite on your iMac the version should be greater than the one listed in that article
EFI and SMC firmware updates for Intel-based Macs
I guess that for Yosemite on your iMac the version should be greater than the one listed in that article