Not many headers for 3SGE non turbos but I found this:
http://www.importmonster....2%20NA%203S%20GE%20set
Dunno how it compares to Fujisubos

Yeah I'm not sure ether
But being 4-1 you would lose some low end I'd assume
I've heard of hurricane headers but not sure if they are any good either

Just heard good things about the super ex fujis

You will achieve nothing appreciable from going to stainless. This is not coming from me, it's coming from 50 years of experience and I am not qualified to argue the point.
 
This is not a blanket statement as there are notable benefits such as, temp and noise control.
 
If you read up on the physics of exhausts there is not a lot you can do past the headers except get the exhaust out ASAP. The best option is no exhaust but since we have to have them, you then have to mitigate the damage of having something downstream of the ports. The whole design is mitigating this degradation of flow bit by bit, but every part you add does more harm by lengthening the time it takes to leave the system. So everything from the ports to the tip is a compromise and it all needs to be considered as a whole, not as individual parts. (I'm sure there are far more qualified engineering experts who would dispute this but this is as simple as I could make it from all the technical crap I've read through).
 
After talking with multiple experienced exhaust fabricators, for most applications there isn't a lot you can do past the headers except reduce restriction. As you eluded, there are different types of performance from different types of headers, but as stated, the factory headers are pretty good for overall. 
 
How much does this matter in the reality of a road going car? SFA. If you like the sound and look, then you've done the best you could hope for.

also another common misconception is when people say "that exhaust is too big I'll lose torque...not enough back pressure bla bla" 
Well I can't see how you can lose torque when all the torque tuning of an N/A motor is done between the head and final collector in the headers...
which also concurs with the above statements by worldwalker.

Amen to that guys

I was never asking whether changing to stainless would improve performance of course it wouldn't it's just a different metal

Yes the stock headers are great design but they can be improved on the argument is now $$ vs performance

There has been some noticeably gains in Na from going to a bigger ID and less restrictive muffler even dyno proven results
Even my 600$ hi flo cat and 2.5 inch cat back had results even I noticed in terms of noise and performance

Each to there own aswell

In terms of exhaust and back pressure in the book mr2 performance by terry heick
It's quoted "I want the least amount of back pressure as possible Na or aspirated I'm more concerned with diameters and bends having it as straight as possible"

:) thanks

I see you've done your homework
That's an awesome book the "MR2 Performance" by Terry.
A++

Yeah first thing I invested in ahah
Very very good read.

Trying to track down a red top for a conversion :)

Already?! Well I guess they are pretty good engines with a glorious sound to boot hehe
Once you got one, mr2.com has a dedicated Beams forum (you prob already know) if you need help or give me a PM as I can advise on what not to do lol
SSS Auto usually has a few greytops hanging around. Redtops bit harder to find local.

Yeah thanks mate

That they are my partners dad that I do a little bit of rally sprints with I sit in and do a little navigating with him he has a old Celica with a black top from an altezza in it that goes pretty hard

Yeah not for a while but when the engine needs replacing ATM it has really good compression 182-190 across all cylinders
What's stock compression 200? Or..

And the old owner had the head rebuilt 25xxxkms ago so should be good for a while but if I do

Ill go a red top. But yeah other then that I'm done until then

It's had an intake exhaust fuel rail was re done and just about to have it tuned and dynod apexi safc

So it should be running pretty well and the most recent thing was coilovers installed :)
Hopefully put out in the hundreds rwkw wait and see I guess engine was looked after pretty well and the compression is still good so it should still have decent power.

But yeah that's the next big plan. I need a better income tho :p heheh

Thanks mate will do if I need a hand with anything