There are many factors that could contribute to heavy steering:
Tyre width - tyre brand/type - tyre pressure - wheel offset - alignment, etc
I have also found that old tyres (harder rubber-less tread flex) give stiffer steering.
 
"I think the popular Nissan GTR and GTST's have 32mm ??"
 
GTR 16x8" (rears) has 30mm offset and GTST 16x7 (front) has 40mm offset.
 
With the GTST, offset is close to the stock 45mm, and if you were to run a 205/50R16 tyre (many people do) it would have a slightly larger rolling diameter that would take it effectively even closer to stock as far as scrub radius is concerned meaning lighter steering, less bump steer, and less tramlining.
On my own car with stock alignment, I found that with them on the front the steering was fairly light (similar to stock). I was using new Brigestone RE 002's that gave zero tramlining even on bad roads.
 
 
 
 
 
 

Hi Nigel,
 
I must apologise, I said 35 offset in my first sentence, but I meant 32 offset, which is detailed in my second sentence.
 
If you plug in the 32 offset in the calculator, it should be closer to being flush. There is still a very small amount of inside clearance from the original guard.
 
The original front stock wheels that came with the SW20 were 15"x6" JJ 45, so if you go to 7" the offset needs to be adjusted to accomodate for the extra width and clearance from the suspension. It took me months to find a set-up that I was happy with (using the calculator), with the performance and looks as well.
 
I'm an MR2 purist, so I try and keep everything as close to stock as possible. 
 
For my tyres, I am running 215/40 (Kuhmo Ecsta ASX) for the fronts, and 235/40 (Falken Azenis FK453) on the rears.
 
Your next challenge will be to find the same brand of tyres for the staggered set-up, with the correct load rating for the rear.  I am looking at the Yokohama ADVAN AD08 for my next set, once the current set wear out.
 
I have no problems with my steering using the above configuration, and the steering is about the same as when I bought it new. Mind you, I have replaced most of the suspension elements in the car, so I expect it to feel like new !! 
 
As recommended by others on this forum, offsets between 32 and 35 should work fine, but the challenge will be finding a staggered set, that you like, with the same offsets front and rear.  This is why I ended up buying the new Work wheels.
 
Cheers,
M

Performance tyres for 16" wheels:
With tyres for the GTST on the front read my previous post
205/50R16 is readily available in different brands.
 
However there is limited choice for the rears if you want to keep stock rolling diameter.
225/50R16's, are readily available in different brands, but you will have a larger rolling diamater (speedo will read 100kph when you are actually doing 104kph).
With GTR wheels on the rear of an SW20 with 225/50R16's, you will need to roll the fenders slightly if your car is lowered.
The only performance tyre that will give you stock rolling diameter that I know is currently available is the 225/45R16 Yokahama AD08R, but there may be others. 
I currently run those on the rear.
 
 

To help understand 'scrub radius'
http://www.racecartuner.com/03/307.html
 

Nigel, suggestion for you.......I don't know where you are in Australia, but if you go to one of the MR2 car meets and see what other people have done, this may allow you to physically inspect their wheel set-ups.  Also, someone may be kind enough to let you have a short drive of their car to see if you like the steering.
 
Hopefully, you'll still find some other MR2 purists around. 
 
Cheers, M

Hi Nigel

Sydney monthly meets thread
https://www.mr2australia...mr2play/tm.aspx?m=80729

The club also has a run or weekend meet up each month. There is a club meet/run next Sunday. Check under the NSW part of the forum for the details.