Hotel Mercure, Arras. 70 miles on the A26, underground parking, easy access, good restaurants and good base for exploring the Somme battlefields. Get the Ride Guide out. There are good roads to be found in the area.
?What about Beauvais? easy access and triangular routes to reims. Other than that Arras is nice, good routes to and from, see wappings routes ?
Either of these work. Arras is 1 hour 15 minutes from Calais, whilst St Quentin is 2 hours 15 minutes from Calais, both straight ‘south’ down the same motorway that you’d take heading ‘south’ to Marseille.
Reading your posts, you want three nights in France, having headed over from Wales (300 miles from Calais) on day one on Friday. I am also conscious that you apparently need to come back to Wales in a day on the Monday, so you want to be reasonably close to Calais (or at least close to a reliable motorway) in order to complete your return journey. Either Arras or St Quentin will allow that, Arras being an hour closer to Calais. Similarly, either will allow you to ride out on Saturday and Sunday into France or Belgium, St Quentin giving you a few different options simply because it’s an hour further ‘south’.
This also assumes you want to be in the same single hotel on the Friday, Saturday and Sunday nights? This has the advantage in that it saves you packing and unpacking each time you move. The other advantage is that it keeps the distance you inevitably have to travel back to Calais on the Monday constant at between 1 hour 15 (Arras) and 2 hours 15 (St Quentin).
If you are looking to move hotels, it opens up a whole heap of other possibilities, it all depends if you are set on ‘south’ and staying in France. For example, you could cut down the journey into France on the Friday considerably if you stayed the first night (Friday) in St Omer. Then on the Saturday, rode on D roads to say Verdun’ish on the Saturday to stay overnight. Then on the Sunday, ride back to St Omer (on different D roads) to St Omer, for the short hop to Calais on the Monday.
Somewhere, you have got to compromise as you are inevitably stuck with the long journey back to north Wales in one day on the Monday. Whether that compromise is staying in one hotel or lobbing in some motorway miles or your proximity to Calais for the first or last nights is up to you.