A458 from Welshpool is brilliant, if you can miss the traffic.
Rode part of this (Dolgellau to Welshpool) a few weeks ago. Agree it's a great ride and one of my favourites.
Try going south from Welshpool to Builth Wells on the A483 (see other routes posted) - cracking!
Did this route today, Easter Sunday 2009, absoluteley fantastic roads. I left home in Stoke about 08.30 and arrived in Dolgellau around 11.30 after enjoying a couple of stops on the way. The roads were a little busy as can be expected but not many caravans so the traffic was easy to pass. Noticed little if any Police presence and can remember seeing any speed cameras. I did not return home the same way but went up to Bala then on to Llangollen then Whitchurch stopped at the Raven Truckstop then Mkt Drayton and home.
Have to agree about the caravans but time it right and you will have a great time.
I HAVE TO AGREE IVE DONE THIS ROUTE A FEW TIMES (CAR AND BIKE) AND YES ITS FRUSTRATING IF YOU GET STUCK BEHIND A CARAVAN NOT MANY OVERTAKING PLACES ESPECAILLY AFTER WELSHPOOL WELL WORTH A TRIP THOUGH
An utterly brilliant biking road, BUT one of the main caravan routes to the Welsh Coast. Go when it's quiet or you'll be frustrated to hell. Basically, Shrewsbury to Welshpool is fast open sweepers, Welshpool to Mallwyd is a fabulous mix of high-speed corners and some fast straights, and Mallwyd to Dolgellau is mountainous with spectacular scenery. If refreshments are required, Welshpool is really the only settlement of note on the whole run.