I have details of two 4-day circular routes of 38.5 and 39 miles length respectively.
One, originally a YHA route, starts and finishes at Llanberis, and includes Snowdon (up by the Ranger, down by the Watkin), Moel Siabod, the southern Carneddau and part of the Glyders range including Tryfan, while it also has lower-level bad weather alternative stretches.
The other is a magazine article; starting and finishing at Beddgelert, it goes over Moel Hebog to arrive at Rhyd Ddu, then up Snowdon by the Ranger and down by the Miners Track, after which it traverses Glyders Fach and Fawr to Capel Curig, and returns all along the Moelwyns to the start.
I'd love to attach the files for anyone's benefit, but I could run into copyright problems. While I personally am not bothered by that, I wouldn't want to get this site into trouble, so if you're not frightened of sending me a PM with an email address I'll send them to you (or anyone else that asks).