I have done the 6 speed conversion with a 3.6:1 ratio diff (standard used under 6 speed cars in europe and australie).
I didn't like it at all.
it felt like i was driving a big truck until the turbo came in at about 4000 rpm.
Ok, topspeed was much higher, but accelaration was gone.
So i changed the diff for a 4.1:1 ratio. That really feels so much better.
The car feels more alive now.
So i wouldnt do the 3.6 diff change.

 

I think the experience with the 3.6 is relative to the torque produced. A 1.6 6psi Greddy is probably "struggling" to get the car moving from a stop. Is your 3.6 ring and pinion for sale?