I've just grabbed a GPX off t'Internet from someone who did it previously, and am examining it using bikehike.
Is the basic deal that you do it as a 400 up the Western leg ( control @YH, continue to Menai Bridge, and loop back to YH again ) grab a bit of kip and then a 200 home down the Eastern leg?
That's it. The YH normally has a bag drop available too (small bags only), which means that you can leave warm clothes there for the evening/night ride up to Menai and back, and clean clothes for the next day. It also has plenty of volunteers (usually well known audaxers) to feed and pamper you. Then up in the morning, a wake-up climb early on, second breakfast of sausage or bacon butties at the next control, a mid-afternoon picnic on the grass opposite the village shop at Weobley and cruise back to the Arrivee in time for a little light supper.
Oh yes, there's the rollers at Llancloudy. I love them - bit of a climb, fast swooping descent, try to keep up the momentum over the top of the next one, rinse, repeat until the final bigger ascent. Lovely
I'm not a fantastic climber, but I don't think there's anything on the BCM that I worry about. The one before the YH you just need to know about or you won't make it up (and if you do decide to walk it's very short and you won't be alone), the one after the forge I had to walk once - I got stopped at the bottom and it was too wet and muddy to get traction to get going again.