There is loads of stuff around that area as you’ve seen. I’ve ridden all the official Cwmcarn stuff, and then the semi adopted off piste stuff at Risca. We did a day last year that was 30km and 1450m of climbing – that was just part of one of the official red loops to get warmed up on way round to the off piste – then shuttling up and down the steep tech. It’s about a 300m ish decent and then turn round and climb back up. Brutal climb – I tend to ride some / push some. Tracks are excellent though. There is also a bit called Network R just along from the adopted Risca trails – I’ve not ridden any of it yet 1 but it’s another grade up in terms of steepness.
Personally if you’re doing say 3 days I’d hit an off piste day first day / uplift day at Dirt Farm or BPW 2nd day / back to off piste 3 rd day. Unless you’re on e-bikes in which case the climbing won’t be an issue.
Im sure someone will be along with a gpx for a big loop (which I’ve not done) – you can join Risca and Willie up I think.
Not too far away you also have Tirpentwys / Barry Sidings / Smilog – none of which I’ve managed to get to yet but all of them look brilliant.
If you look on Trailforks some of the off piste is showing on there – definitely the adopted off piste at Risca.