>> snip >>
>Disadvantages are:<< snip >> less grip << snip>> higher gearing, inaccurate
speedo << snip>>

Based on my observations:

I've noticed increased grip with my 27x8.5 R 14 tires.  I have more tread
which means increased footprint.

Higher gearing is not necessarily a disadvantage.  I welcome the lower
engine RPM on the highway. I don't notice  much difference in power in the
hills or difference in the mileage.

Inaccurate speedo?  My Westy speedometer read high as is the case in a lot
of Vanagons.  The taller tires corrected this error.  This has been verified
by radar and my stop watch.

Chris.