The Eildons and surrounding hills are wet, and muddy. The St Cuthberts Way comes past my front door, and yesterday a load of runners were doing some event, and it looked serious muddy.
As youngrob says, the Brethren and around was also muddy off-piste, at least yesterday when we were up.
I’d avoid Gypsy Glen too, as the feeders in will be pretty crap.
For a cx bike I’d look at the Southern Upland Way, but specifically from over Duns way across to Melrose via Lauder. Its pretty much all surfaced tracks and would really suit a cx bike.
Or just GT and Inners, which tbh is what we do when the natural stuff is crap.
Where, and how long, are you staying?