I have the potential for some summer accommodation in Bonneville, and they suggest riding in the Aravis region around St Jean de Sixt . Anyone have any experience riding there, apparently the neighbouring villages of Le Grand Bornand and La Clusaz (both 3km away) operate ski lifts from June to September. IS this riding likely to be any good Singletracky fun…

Yep, the riding is really good. As it’s quite low it’s generally rooty singletrack rather than big exposed trail but there’s a few of those knocking about too. It’s not the biggest area in the world but there’re enough waymarked trails to keep you happy for a week or two and plenty more that aren’t marked. There are only a few lifts that are open one to the top of Mont Lachat from Grand Bornand, One to the top of the Plateau de Beauregard and two chairlifts to get you to the top of the Crete de Loup. There’s also a couple over towards Manigod but that’s a bit more limited.

Some top quality rooty nonsense can be found on the beauregard loop and on the Tete du Danay. There’s also a brilliant loop up from Petite Bornand to the Plateau de Glieres (definitely worth a visit anyway) and back via the Chalets des Auges and the there and back to the Lac du Lessy is supposed to be awesome fun but very tough.

The Grand Bornand tourist office sells a map of the waymarked trails for a few €s – mostly XC loops with a few DH-ish trails (those are from the La Clusaz lift I think).

cluzas is def worth a visit. the marked trails are fun but there are not that many. Good for a day or two before you need to do some exploring.
As with most areas, there is def some decent singletrack to be had if you get an IGN map.
The marked trails I rode a La Grand Bornand were not great (6 years ago) but may have got better. And some exploring with IGN could help.
You’re only 2hrs drive from Morzine etc is you fancy a change of scenery.
And there is also some decent riding to be had in the Les Saises area (other side of the valley SE? from Cluzas)