I too had been lured by the look and apparent toughness of the larger,
off-road tires - I had Goodyear ATs - and found them to be problematic.
They gave my Syncro a little more ground clearance, but seriously affected
my ability to climb long hills and maintain way in the high winds around
here (southern Nevada and Utah).  I have gone back to 205/70X14s - Michelin
MXTs - which are very high-rated (1709 lbs per tire) compared to the ATs
(1518 lbs), and the difference in vehicle performance is significantly
improved with little loss of off-road performance.  And I don't have to
slip the clutch nearly as much.  I find these tires a much better choice -
and I still go all over off-road

Original Message:

I just put on 27x8.5x14's on my Multivan.  I went with the Bridgestone
AT's.  I did this as we plan to take the van to as many out of the way
places as it will take us, this includes dirt roads in Death Valley -
our favorite camping place in the world!  The difference is 5% for me.
 I checked this out with a friends GPS.  When the speedo shows 61 mph,
I'm going 65 mph.

What I really noticed is a drop in torque.  I now need to be in thrid
to climb hills that I used to be able to climb in forth.
Unfortunately for me there are a lot of hills in the area which I live
in!  On the flip side, cruising on flat lands, slight inclines or downhill
the engine turns a little quieter.