I thought it was a rather timid climb that way, it is just the short bit up and round from the hotel that is of note. The climb up from Beddgelert is more substantial.
Pen-y-Pass Youth Hostel is at about 359m.
Beddgelert is about 50m
Capel Curig is about 190m
So yes, the Beddgellery ascent (The BCM600 route), while being quite a long road (12km to the Hotel turn), gains around 300m
The hotel turn, for the final climb is about 276m.
That final climb is 1.6km, from 276m to 359m.
I started to get cramp in the "Glutes" just as I approached the turning, I'm just not used to long, relentless uphills like that, even if they aren't incredibly steep.