Done it a few times at various spots. Dialled Alpine worked a treat.
Morgins, Alp d Huez, Swiss National and “off the beaten track” stuff were wonderful on a hardtail.
The Pleny hill had some absolutely brutal sections (that “10 percent” bit for example) and the Black runs at Chatel were really tough, again due to the braking bumps.
I used some big, fat 150mm forks rather than 120mm though. Just meant I could be a bit lazier when I was really tired and have more chance of getting away with stuff.
Its good fun, but if you want to go properly fast then I guess a downhill bike is your best bet. But since you;re even considering going on a hardtail, I’d imagine you;re a half decent rider, so you’ll still end up overtaking all the shite folk on the “all mountain” style bikes.