Agree with Bob, last year in fairly good conditions, though clag above 8-900m a lot of people got lost. Even last week in a race in the Carneddau some muppets got lost..(me)
It does get very spread out, I normally only ever see 2 or 3 people on this race. The first part on the Carneddau is worth a recce.
From the Bera's to Carnedd dafydd I'd keep the map out. The top of the Glyders section is also a bit nasty, only a few hundred metres long but enough that you can lose a lot of time and I've known even local runners get very lost.