Use the warmers, skip the slicks unless you can keep up with Derek Leslie, Chris Moon, Pitzer, DJ, Floyd, Bob Blandford, Mark Sterns, Drew Harbuck, Buck Miller, or Peanut. Those are the fastest Control Riders I've met in my time with NESBA (7 years now).
I tried slicks after I got my warmers in 2007. Didn't really notice the difference between DC3's and the slicks, except the cost and slicks seem more sensitive to suspension. DC3's are enough tire for 80% of us.
The warmers will let you set your pressure correctly before you go out. (33psi HOT has been optimal for me). They'll also allow you to know your tires are more likely to be at operating temperature when you go out on that first lap.
Last year was my first season in I group, and it was a tremendous year of learning for me. I did it all on the DC3's, and I plan on continuing to run those tires for quite some time. I've been in situations where I thought there was no way the tires were going to hold..and they never broke loose on me.
I usually run a set for like 5 track days, then retire them to sell to some street rider for like $50-$75 set so I recover some tire cost, and they don't get ripped off for $500+ for a set of tires from a dealership.