165/185 tuning: If your happy to boost below factory fuel cut of your stock ECU and keep the factory turbo, then the following need not apply (220-250bhp).
for afm equipped cars: > rewiring the loom to accept any ecu be it a later toyota denso unit or aftermarket incurs the same labour cost or time invested.
st205 / sw20 ecu swap fine if you want factory faff power and have the 205 head, turbo and inlet to match the VE of the system for which it was mapped 0.8 -1.1 bar (260-300bhp).
imoc.co.uk highlights that rev2 > rev3 ECU conversions alone and original engine do NOT deliver. (ECU is mapped for different VE of later revision cylinder head and induction etc)
A rev 3 ECU is 14 year old ++ technology. The toyota units cannot currently be matched to new mods / different VE charactoristics. (That said search MR2 forums for user JMR_AW11 the denso ECU hacker

)
The toyota ecu works very very well within its detuned stock parameters and has many many on board safety features to deliver 200,000+ miles on a factory set up. however (currently)it is not flexible enough to deliver the bang for buck of a mappable unit + modified car scenario.
After market ECU is not just about mega power, its about implementing a modern engine management system that is on par with today 2 litres turbos (fodders

).
advatages: >>>improved economy & performance, on board boost control strategys, datalogging of all temps (parameters) with soft cut safety strategys to protect your engine, water injection, anti lag etc etc and the option to wind up the boost as far as you dare or your fuelling and cooling mods permit

ECU should be modification #1
# Its a long term investment that can handle whatever mods your budget permits. The bonus is that when it all goes wrong due to worn stock engine parts etc The engine will be scrapped / broken, but the ECU will always be worth good money when it come to selling up or can be taken to a new project.
# Aftermarket ECU will suffer very little depreciation and will pay for itself in the long term on fuel savings alone.....(lesson i have learned long and hard. 4 years and many ££££ @ 12-16 mpg on stock ECU + AFM & basic performance bolt ons.)
# A well mapped and developed aftermarket ECU set up can deliver in excess of 330 bhp and 330 ft/lbs on stock internals, stock 430 injectors, stock CTxx turbo, made reliable with water, oil and charge cooling upgrades. You will need to wind up the boost quite high to get this...21 psi +++
# Downside: 165 & 185 still need new brakes and suspension

to enjoy the new found power....
All i will say is that tuning old toyotas is very expensive. more power = more heat and quicker wear on all moving parts, not forgetting the need to replace like for like a mountain of worn out factory components that have perished due to old age...
:

.....thats the way i see it.