I have bikepacked and bivouacked the Southern section of the Ridgeway a couple of times. Avebury to Goring-on-Thames and back. The Northern section beyond that is prohibited to bikes as it is a footpath. But the aforementioned section is best anyway. There are plenty of Roman and Neolithic goodies to see up there.
You're making me nostalgic again, Heltor. I grew up in Kingsclere, south-east from Newbury, and once I was old enough to go out on my own I liked to ride up to the Ridgeway, usually on the Wantage road, then along the top plunging down all the rutted drops at terrifying speed, eventually heading home along the Lambourn valley. There were many variations, but that would probably have been the favourite.
Another typical ride went further westwards to Hungerford, then south to a very similar ancient hilltop way which at the time I called the southern ridgeway. It passes Inkpen Beacon and Walbury Hill, the highest chalk hill in Britain, places which some will know. The section which I used to cycle is shorter than the Ridgeway; if I were to say it's better then I'm clearly being biased, but it can't be denied that it has features the Ridgeway would envy.
What never occurred to me at the time was to try and link the two. I'd yet to develop that kind of vision.
If you leave the Ridgeway at Avebury there's a section of another track called the Wessex Ridgeway leading to Marlborough. From there you can follow the Grand Avenue through Savernake Forest, after which a few miles of lanes take you to the ridge of the North Hampshire Downs. Here's what a route might look like - 105.8 miles:
https://ridewithgps.com/routes/31447787?beta=false
I've started in Kingsclere so that I could begin with some nice lanes to Streatley and the start of the cycleable part of the Ridgeway. Avebury would also be a good starting point. The loop hanging off the bottom includes Chute Causeway, a section of Roman road at a point where even the Romans couldn't keep it straight. I don't know it but it looks intriguing and I think it would enhance the ride.
I was going to say I can't do this now as I don't have a suitable bike. But the bike I used to use in the 1970s was a lead-framed three-speed Sturmey Archer jobby, and I didn't see anything wrong with that at the time.