They are pretty steep. From memory the one up from Castley isn’t well marked on the ground though obviously things change.
There are two routes up via Winder, one starts from Lockbank Farm and apart from the start is steady away. The other starts from further along the lane towards Birkhaw (at about the high point of the lane) and is rideable if dry as there are some very steep bits – in normal conditions it’s about 90% rideable.
Edit: Just checked the 1:25K map and both these routes up Winder show the bridleways taking a different line than what exists on the ground. The route from the farm is better following the track by the wall then cutting back – the direct line shown is steep. The other bridleway is shown cutting across the upper slopes of Winder, this simply doesn’t exist on the ground.