In reply to benp1:
Yes, a North start gives you the options of Tryfan N ridge, Bristly ridge and Crib Goch in ascent (as well as the small scramble over Castell y gwynt).
Bwlch y ddeufaen above Rowen gives a more direct start than the routes from above Aber, though the Anafon valley is nice.
The route over the Carneddau is a straightforward peak to peak route apart from the dog leg for Yr Elen. Definitely DON't try the direct descent down the S ridge of PyOW, take the East ridge to Glan Dena.
The glyderau route is fine - the only detour being to miss out Bristly if you don't fancy it. There is a slight difficulty at the moment as the bridge over Afon dudodyn has washed away so you'll have to get across the river.
There is always a part of the route from Nant Peris along the road, the distance depending on which route you want to take. North Ridge of Crib Goch is the obvious one for a N-S 3000s and involves a couple of km along the road up the pass (partly on a footpath over the wall on the S side of the road).
At the moment everywhere is quite dry (this doesn't really affect the 3000s route unless you need water at the spring on Yr Elen), but probably all going to change in the next few days. Midges have been bad this year but most of the route is on exposed tops or ridges and even a slight breeze keeps them away, especially if you keep moving.
Post edited at 18:04