I have a Mitsu GTO, mine is an Mk1 1993 Twin Turbo and I love it to death heheh... roadtax in West Malaysia is RM 2060 per year, but my GTO buddy in Kuching, Sarawak only pays RM987 per year (freaking half price!)
Main things to do when you first get one: overhaul/rebuild the 6G72 TT engine, check wiring + ECU and the ignition system, and check the interior components as well...
This car is a match anytime for Supras and Skyline, though it is under-rated in a way, its got a damn loyal following in UK. Japan, USA.
Main parts/tuning houses for the GTO: PitRoadM (Japan), and 3SX (USA), Nelson Performance (USA) ... check out vids on youtube
In stock form the VR-4 Twin Turbo GTO makes 316bhp and 427Nm of torque, (stock 0.8 Bar boost). increasing the boost to 1.1 bar can easily unleash 360bhp and 480Nm of torque.. so imagine if those twin TD04-9B turbines are replace with bigger TD04-D750 or TD05-G units... 750bhp GTOs (called 3000GT in the USA) are common in the USA, and yes there are 1200hp GTO's on youtube (also from the USA) so the potential of the 6G72 engine is definitely on par with the 2JZ in the Supra or the RB in the Skyline..
PitRoadM's Hayabusa GTO has 920Bhp, and has taken pole many times in Super tuner battles..
Be prepared to spend about RM15k for the first year, to change parts, tune, repair (local chopshops always give a high price 'coz its rare' - bullshit gimmick), UK and US has a lot of parts available on Ebay...
like any other Jap sports car, you have to spend on good parts and upgrades to get it running good.. don't be stingy and cut corners, the problems will come back
If you go the GTO path, you can always pm me for advise on the car, more than willing to help a fellow GTO owner :)