more of a scenic route than one for a quick blast due to too many villages and speed limits and if you do go as far as st davids go to whitesands bay as the ice cream is GREAT
The run on to St Davids is good, quite tight though, ideal for 400/supermoto, litre supersports would be a bit of a handful. Cracking ice cream at The Bench in St Davids! There is a small B road from Fishgaurd to Rosebush/Preseli Mountain which is a great blast, very intense with some sharp corners and a few suprises, gets the heart rate up.
I imagine staying on the A487, & riding to Fishguard & on to St Davids would be great as well.
Head South from Aber (well worth a visit- park on the seafront for free) on the A487 - Some straight stretches, some long bends. This stretch follows the coast with views over Cardigan bay off the cliffs, you can see along the coast for miles. Quite a fast road, plenty of places to overtake. Good road surface. At Synod Inn, take a VERY sharp left, heading along the A486 towards Llandysul. The roads here consist almost completely of bends. After Llandysul, the roads become wider, more places to overtake, faster sweeping bends and excellent rpad surface. Look out for the speed camera just before you join Carmarthen.