Going back to you mentioning your friend seeing smoke coming out of the exhaust, if the color was black then I wouldn't worry too much. Your car may just running a bit rich. My friend's ep3 used 5w30 castrol edge and I also see black soot coming from his car when his hit VTEC. I won't be surprised if I had black soot too.
I think it's fine as long it's not blowing blue/grey smoke.