These cars should have no problems running in the 10s with the 427 motors. My friends 01 WS6 Trans Am(running at full weight) ran an 11.7 at 114. Car had a stock 346 c.i. LS1 short block, cnc'ed ls6 heads, comp 224/230 cam, 3800 stall, 3.73s, lower control arms and a set of mickey thompson e.t. streets. It was built by Mike and Ron at Vengeance Racing. They were the guys that built the Dick Harrell/ZL1 cars for GMMG. It dynoed a little over 400 to the tires. The automatic phase III ZL1s shouldn't have any problems getting into the tens. With the 6 speed cars, its up to the driver/traction. A little side note here, Ron and Mike are squeazing 500 rwhp out of stock ls1 short blocks now.
They posted up a thread on ls1 tech a while back of an 02 SS with a 6 speed putting down 503 rwhp with heads, cam fast 90/90 setup, bigger injectors and a tune.