I am going to buy a Roadster soon. Are there any tonal differences between a combo and a head other than the cab? I know the combo is open backed, does that hurt the sound quality much? I assume the combo can be hooked up to a 4X12 cab. I have a rectifier cab and may buy the combo just for the fact that for smaller places I wouldn't have to lug around the 4x12. Thanks for your thoughts.