lol, that's a previous model stang. 00-04. Put it up against a 05+ with a blower and it gets raped in the ass.
Besides, that looks and sounds like an 03-04 cobra, not a GT. Probably stock or close to stock. 390hp. weighs about 3800 lbs. Still, you can easily tell that it's top end power is way better than the sti as it gains on it the whole race, and passes it up.
I could post countless video of 05+ mustangs at the track beating sti's, and countless sti's beating supercharged mustangs. There's no "proof" in doing this.
A stock 2008 mustang gt with the addition of a whipple supercharger at 10 lbs of boost, a standard for H.O. systems, puts the car at 500hp for 30K. Put some sticky tires on back with a 4.10 gear, you're sitting at 31K, which would not only smoke the STI off the line, but also give it no chance at ever catching up. It would murder an STI. So, if you want to play the $ for $ game, the mustang would easily beat an sti in an acceleration match. Because 8 grand in upgrades still doesn't even match the retail price of an STI.
To get an STI to 500hp, you have to take the whole engine apart and upgrade every component so it can withstand 20+ lbs of boost. Upgrade the intercooler, new turbocharger, new internals which would cost about 10 grand. Plus the labor would be a huge bill in itself.
Using drag racing videos against a mustang, which is designed for such things, isn't a very stong tactic.
I raced my friends '06 sti from a roll when my '07 stang was stock, and we we're dead even the whole way up to 120ish, with me actually slightly gaining in the top end. Off the line i didn't have a chance, but actual acceleration power minus the traction issue, it was very comparable.
Obviously, around a track an STI would absolutely destroy a mustang.