If you’re used to riding on big mountains in NZ I’d imagine Delamere might be a bit disappointing as there’s not much elevation.
Llandegla would be your closest & best option especially if you like getting your wheels off the ground.
For more technical physically demanding big bloody grin on your face bouncing over rocks as fast as you can fun…the Beast of Brenin trail (38km) at Coed y Brenin is hard to beat. There’s a brilliant cafe half way round that serves the most f’kin amazing scones.
Don’t know what bike you’ve borrowed but in case you’re worried about breaking it both llandegla and CyB hire out reasonable spec bikes.