I keep coming back to this thread.
If I read this right, then your current choices are either a V70 DRIVe or no V70 at all inasmuch as you place great importance upon fuel economy, and inasmuch as the V70 DRIVe offers by far the best mpg amongst the V70s that fall within your budget.
Would it therefore be wrong for me to suggest that you also consider reliability since great fuel economy is only of value if engine maintenance isn't excessively costly.
(I took Tatsfield's advice and googled the DV6 engine, and it has both strong proponents and strong opponents.)