On the off chance I have misunderstood this... 

(background)

About a year ago we jumped from the faithful to get access to Spark's 700MHz 4g upgrades in our area.  W

hile no provider has coverage at all at our house, we often on the road and we were roaming on Vodafone or on a 3G 2degrees.  Speeds ok on both, but then we often had problems going between roaming and home network, and then Spark's network and its speed on Skinny was too tempting and that was that.  

Happily set up there now and found locally there are fewer blackspots than when roaming on Vodafone 

Now Vodafone has 700MHz in our area too (it didn't when we jumped ship).  Do 2degree customers roam onto 700MHz 4G from Vodafone?  Is the 3G 900MHz speed limited when roaming?