This Navcore works great on my Go300. It has been "lightened" to give more free memory. I'm able to use computer voices without any lag with this. Also you will be able to use maps with Advanced lane Guidance & IQ Routing.
Thanks to Carman for making it available.
P.S. You dont have to update your bootloader to use this Navcore. I did update mine so as I could use the larger SDHC cards. Be aware, there is a risk flashing the bootloader. Make sure you know exactly what you are doing, if you decide to do it.