I actually ran a Charger Scat Pack this weekend with a tune on 93 oct and some mild weight reduction. My mods are on the sig below.
We were dead even till 140 when we shut it down. Probably one of the best races I've ever had. Neither one of us would pull away from each other. Shook hands and called it a tie. That same night I ran a stock 6th gen Camaro SS with the rear seats/spare tire removed and beat him by about a car or so from 40-140. The Charger ran him as well, with the same outcome.
In short, yes an IS20 GTI can at least hang with a stock scat pack Charger, as long as it is properly tuned/modded.
Nice man! That tune sounds like it's hitting all the right notes.