I have a 3:89 with an OD and am very happy with the combo. It depends on
what you want the car for.
Assume you never turn on the OD. The 4.22 will be quicker and put less
stress on the car from loading (though perhaps more stress because you will
find yourself driving harder ;-) The top speed will be lower on the
Now, when you add the OD, the 4.22 with OD will have a lower rpm at 65+
than the 3.89 without OD. But, the 3.89 with OD will have an even lower
rpm at 65+.
So, what do you want more quickness or even lower rpm on the freeway?
I chose the lower rpm on the freeway. That's where my car is the most, and
especially here in Los Angeles, where the speeds are closer to 70 and up,
the lower rpm made sense. If you won't be on the freeway as much, the 4.22
might make more sense. I also have the Holbay engine which makes up for
any lower rpm issues.
It has been said that the 3.89 OD combo will cause the engine to lug too
much when in 4th OD. On the other hand, if you are mindful of it and
downshift before accelerating or taking on too much of a mountain, I figure
you will be fine. I have not noticed any issues with the engine losing any
sort of power - but, then that could be because of the Holbay breathing and
power in the upper ranges.