Torino - Nice Rally

I’m thinking about this for next year, was planning to ride my new “gravel” bike, takes up to a 50mm tyre.
How long does it usually take?

I rode it in 2018 on a gravel bike (on 47mm WTB Horizons), which felt like a good compromise, and I'd probably choose a gravel bike again. There's a lot of road miles and a LOT of climbing. Any smaller than a 40c tyre would have been tough going on some of the rougher gravel sectors. I'm sure a mtb with fast rolling tyres would get you round absolutely fine too though.

I did it on rigid mtb with 2.1 tyres. Was a great choice for the rougher bits (via de sale, etc), less good for the road bits. Tyre choice is probably most important - wouldn't want to go narrower than 47.
Majority of people were doing it on gravel bikes but you'll be fine with either. Lowest gearing possible is main thing, there is a lot of steep climbing.
Think I took 8 days, most people did it in 6 or 7. But basically you want to take as long as you can get away with - the longer you have, the more opportunity for leisurely meals, etc. The route's flexible enough that you can adjust it as you go along depending on time limits. If I'd had more time I'd have detoured to Molini di Triora. Whatever you do don't miss Via di Sale.
Personally I'd sacrifice time in Nice for more time on the route - Nice (for me anyway) was horrible and overcrowded after being out in the mountains and was glad I only stopped there briefly before heading to the airport. On the other hand Turin is a nice place to spend time beforehand.
Would love to do it again - don't think I've met anyone that's done it who hasn't had an amazing time.

(have probably spammed my photos on here before, but if not - https://www.flickr.com/photos/adownie/albums/72157711147121713)

Agree with the other answers here, I used a rigid 29er with WTB Nano 2.1s which was pretty ideal. Lots of gears and big fast tyres is the move.