You can beat stock V8 Mustangs with far less than that.
Years back, I was riding with a friend of mine who had a 354 whp SS/TC and we beat a fully-bolted-on (everything short of cams or boost), and even though he missed third and leisurely fixed the error, the Mustang still never passed us.
For what it's worth, the current Mustang, with the V6 is probably the fastest V6-powered Mustang you can buy, and they only run low 14s, stock.
On a run where I didn't launch worth shit (on 195/60R15 all-seasons), and with the speed-sapping automatic (it's great down low - but with only four gears, it loses a bit at top end due to being in direct drive and then overdrive), I still ran a 14.1. I'm only around 250 whp (if the torque converter would lock during a run).
In "other situations", I've beat a 3-valve that at least had an exhaust. If it kept going, I probably would have gotten passed, due to the aforementioned gearing, but down low, that didn't happen.
So you probably don't need 4-500 whp...probably...to beat up on a typical stock V8 Mustang, because you have a huge weight advantage. A stock non-SS Cobalt will weigh in around 2800 or less. Mine, with the supercharger, my sub box/amp/subs and a good amount of fuel only weighed 2850 lbs.