Well, first off was your top up or down? If it was down that'll drop the car's performance 2-3 tenths. The roadster runs a little slower than the coupe just because of the rag top causing more drag than smooth metal, about another 2 tenths (compared to another SRT-6).

I'd look first @ getting an intake on the car. Then maybe a 178 or 181mm pulley and Inmotion tune (really cause it's $300 cheaper than a LET tune and hte results are about same). Sooo, it'll be around $1,800 for all of it.