I have been researcing to buy a right unit for me for past month, and I have come down to f900bt, f90bt, or x910 bt. I will be upgrading the firmware for f series as soon as I buy them, but I can't find the store that sells the upgrade card for $60 anymore. Since the prices are $400, $500, and $600 for f900, f90, and x910, I don't know which one is the best choice. BTw x910 will be new unit, and others will be refurbished.

Would spending extra $200 worth it over f series? or is it better to just get refurbished ones with firmware upgrade?