I raced one of the new 5.0's a few months back, dealer plates mind you so it wasn't a sold car, and it wasn't much of a race. He was stuck behind me in the express lane. I put it to the floor from 4th gear and let the rpm's just climb. He stayed on my ass. I rolled it into 5th and kept it to the floor, I didn't care about highway patrol, as long as the lane ahead of me stayed empty this was going to happen. He stayed on my ass. The SCT Livewire reads off the PCM, and the livewire said 165 but wasn't moving past that. The tach kept going, and I did finally left off at 6k/rpm.
That damn 5.0 stayed on my ass the entire time, of course. I got home and did the math on the gear calculator, if I'm not mistaken 6,000 rpm's w/4.10's on 275/40/18's turns 173mph on the speedo. Ford's speed sensor in the GT's apparently maxes out at 165, which is why the livewire didn't pick up anything past 165 on the digital.
For the S197 IMHO 160-170 is topped out without a blower.