5C isn't bad, love mine! I have 2 friends with 4c's. One of them is running 6.80's on a 100 shot and that's on 18" wheels with a radial.
Man, Your times in your sig NA is crazy too. I wished I could keep it NA so I didn't have to hear all the "bet you wont run me off the bottle" bs.
Your friend on the 100 shot, do you know what his mods are? Is it mostly stock with a converter with nitrous? If he did E85 and a 150 shot, I would assume he would be in the low 6s.. Which would be incredible.