Is it worth the extra price for the 553ELX? I currently have a 500CM and lenses, would like to add the extra features of the motor drive and electronic release. I understand that I will need to also purchase a 9 volt battery converter. How hard is it to find a nice long cable release for this? What about a remote release? It would be nice to be able to go 20+ feet, more would be better. I assume it will work in bulb mode as well.