My advice would be to keep your eye out for me, 'cos I happen to be walking this on Saturday as a warm-up for running it with the Vegans next month (when you say 'steady day', do you mean a steady day's running?)
Three of us will be starting from PYP at approx 4am, and doing C.Goch first, then G. Ugain and Snowdon.
Prefered descent from Snowdon:
"Walk down the Llanberis path, veer off behind Clogwyn Station, follow the railway track down through ‘Rocky Valley’ and you will see a fence on your left bordering the steep ground that drops to Nant Peris. Follow this fence until it veers right, and there lies a little stile. The stile marks the start of a faint path down to Gwastadnant that it quite steep but not punishingly so. It ends at the bank of the Afon Nant Peris very close to the footbridge at SH 608 579. Job’s a good ‘un"
For descending Tryfan, we always drop back down the south ridge, veering right a little to pick up a scree gully that takes you down nearly the shores of Llyn Bochllwyd, it's indirect but not so steep.
My report of a walking version, including further route description and lots of nice photos here:
http://www.walkingforum.co.uk/index.php?topic=14564.0
We raised £1240 for MRT.