I ran the setup you described: Steeda adjustible quadrant, firewall adjuster and Spec 2+ kit for about 50k miles with ~400 whp and no issues.
When I installed mine, I adjusted the part where it goes to the clutch fork as tight as I could get it and then used the quadrant slot closest to the firewall (mine had 2 slots) and adjusted the slack out at the firewall and it may have been 1/2" adjusted out.
The pedal had about 1/4 to 1/8" slack with the cable when I was done.
The guy I sold my car to has been running it for ~7,000 miles + also with no issues.
The only thing to mention was the Spec t/o bearing failed shortly after install in my case (it squealed), but a new t/o bearing fixed that. =)