They are very very similar...
STI is a touch faster, EVO8 handles better.
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Subaru Impreza WRX STI
Curb Weight: 3263 lbs
Layout: Front-Engine/AWD
Transmission: 6-Speed Manual
Engine
Type: Turbocharged Flat-4
Displacement: 2457 cc
Horsepower: 300 bhp @ 6000 rpm
Torque: 300 lb-ft @ 4000 rpm
Redline: 7000 rpm
Performance
0-60 mph: 4.8 sec
0-100 mph: 12.9 sec
Quarter Mile: 13.2 sec @ 104 mph
Skidpad: .--g
Top Speed: --- mph
Braking, 60-0 mph: 111 ft
Slalom Speed: 69.1 mph
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Mitsubishi Lancer Evolution VIII
Curb Weight: 3263 lbs
Layout: Front-Engine/AWD
Transmission: 5-Speed Manual
Engine
Type: Turbocharged Inline-4
Displacement: 1997 cc
Horsepower: 271 bhp @ 6500 rpm
Torque: 273 lb-ft @ 3500 rpm
Redline: 7000 rpm
Performance
0-60 mph: 4.7 sec
0-100 mph: 12.45 sec
Quarter Mile: 13.08 sec @ 105 mph
Skidpad: .98g
Top Speed: 155 mph
Braking, 60-0 mph: 106 ft
Slalom Speed: 71.4 mph
*stats taken here:
http://fast-autos.net/makes.html
**not sure why they listed the STI's 0-60 at 4.8, it should be 4.6