Depends on how cold it gets where you live.  Out here in Arizona's
warm country I've not found the slightest difference between a 650 and
850 battery, other things equal.  In cold weather the battery capacity
goes way down,don't recall just how much, but it loses half it
capacity on a cold winter day in Rochester NY, that would only give
you a little over 300 amps.  Might not be enough to get that thick oil
moving very well making it hard to crank.  And as the battery ages it
will lose more and more capacity.