Cycling the South Downs Way on a gravel bike!?

Did the SDW with a friend last year. Both used gravel bikes. I ran 650x42 tyres and didn't feel that a mountain bike was needed on the route. Lucky that it was dry at the end of Sept. My friend suffered one puncture on a descent running some 700x38 tyres. I really enjoyed it and I'm planning to head back with a bivi or tent to explore the area some more later in the year. 

A few pics here

I did Winchester to Eastbourne in a day on a Specialised Hard Rock hard tail back in 2010. It took me over 13.5 hours and I was proper knackered at the end of it!  I remember thinking if I ever did it again I would want to do it on a full susser, the extra weight worth it for the comfort.

A friend of mine tried a Wiggle event a few years ago on his cross bike; the route was meant to be 60% road, 30% gravel and 10% proper off road, on the South Downs.  On the flinty sections near Bignor he shredded his tyres and had to abandon.  I suspect they weren't very suitable for the terrain, but will ask him if he can remember.

I still have the Hard Rock and am thinking about trying it again next year, as it will be 10 years since I did it before.  It has 2.3" Specialised Ground control tyres, which are better suited to muddy conditions than the dry ones we have at the moment, but I can't be bothered with the faff of having two sets of tyres, I'd rather be out riding than swapping them over.

As others have said, the weather on the day and the week before can make a huge difference.  I live about half way along so know where the boggy bits are going to be; at the moment it is pretty dry on the bits near me so should be ok on most tryes.

There's a cafe and bike maintenance point at Sullington Barns now; you have to descend off the top to get to it, but there was a reasonable selection of tools there last time I looked.  This is around the half way point, before Steyning.

I've done it a few times. My advice is to be very careful of the large flints on the descents. One threw my brother off his bike at speed. And that comment about slippery when wet - I totally agree.

Back before "gravel bikes" were even a twinkle in the marketing team's eye I did it -  Winchester - Eastbourne - on a Edinburgh Bike Coop drop bar tourer sans rack and mudguards. For the craic.

@FestaG makes various good points above.

Eminently do-able on any bike with a degree of off-road capability providing it is ridden within its capabilities.

I did the South Downs Way Century in 2017 on an aluminium Fuji CX 1.1 (i.e a gravel bike), having previously done Winchester to Amberley one day and Amberley to Eastbourne another.

The full ride was tough, and I certainly wouldn't have fancied riding back the next day, but then I was at the limit (probably past my limit!!) of stamina - sounds like you are at a higher level.

I used WTB Nana 40mm tubeless tyres for all that (on Stans Grail rims/Hope Pro 4 hubs), 700C size. Due to the minimal amount of tarmac and several rocky descents I would recommend something a bit knoblier than a "gravel" tyre, and go as wide as your frame will allow. I did get one puncture I was aware of but the tubeless sealant did it's job. Probably got several other knicks I didn't even know about. 

I have ridden up there in the wet and it's really difficult/dangerous - the top surface of the chalk becomes extremely slippery, so if you can be flexible make sure you go after a dry spell.

It's an amazing envirnment to cycle in, have a great trip!!