I think that it will depend on the coordination of the CoW. If they coordinate well, Spulla won't be able to do much. Speaker has a ton of MP experience which will help (when does he get back from his hiatus?). I do not think they will be able to wipe out Spulla, but I'd be surprised if they defend without any cities lost.
Of course, the other consideration is that once the initial stacks are dealt with, it will be much harder for reins to come all the way from the more distant CoW members so it may leave Jowy vulnerable.
Of course, the other consideration is that once the initial stacks are dealt with, it will be much harder for reins to come all the way from the more distant CoW members so it may leave Jowy vulnerable.