I used to live near the SDW and I can attest it will be a (very) hard ride. I’ve not ridden much of it but some of the climbs up and down Old Winchester hill area are outrageously steep. I think it gets shallower after that (the descent of Butser not much later is really “fun” on a ‘cross bike!)
I was looking into their off road London to Brighton route a few weeks back and might look into doing that, or a similar route if it’s too full.
I’ll think about giving this one a go, but I think it might be a step too far for me at the moment- I’ve read the SDW can be very punishing to ‘cross bikes due to the jagged flints that abound, and when wet the chalk becomes very slippy.