Seems to me that is dependent on how large a slice of spectrum they have. But, all things equal, a 20MHz "slice" of 700 will propagate further and penetrate structures better, but wouldn't have the capacity of a similar "slice" of 1700.
I do agree that Digicel needs to sort out their network mix. But, I kinda tongue in cheek suggested Digi get out of the network end and just become an MVNO of sorts. LOL