This is kind of an ironic post for me......reason being is my best friend has an 06 Spec5 and I have a ZX3. Now granted my ZX3 isn't a SVT and Im not sure how they stack up versus a Spec5 but I will tell you this, my ZX3 has alot of bolt on mods in the engine bay along with a brand new 6 puck racing clutch and lightweight flywheel, ford racing sport springs and some low pro tires, and from 0 - 90 we are dead even in a drag race, from 90 on, it's like I slammed the brakes on cause he walks the dog with me. Now onto a little country road driving, I can't stay in sight of his Spec5....honest to God! When I lived in Kentucky I just lived about 3 houses down from him and we both knew the roads like the back of our hands so there was no advantage there. Now your prolly asking yourself, what all does he have done to his car.....right........He is sitting at stock height, rolling some 17's ( same as me ) and a 40 series tire vs my 45. Motor wise, he is running a full CAI and NGK plugs and wires........THATS ALL!!!!!
Honestly though, if it were me, I would go SVT all the way. Reason being is, Ford somewhat supports a performance side to their cars and trucks......KIA on the other hand not so much. Don't get me wrong though, you can get things ( KFX ) for the Spec5 but your bank book will wonder what the hell happened not to mention normally there is a crazy wait after you order your part, they say it's cause everything has to come from Korea.
Here is a pic of his Spec5. The first time I seen it, I was like WTF.....why would you do something to a KIA, that was before he spanked my 92 Integra
Good luck with whatever you choose though. Hope this helps some.