Bonjour tous le monde.
I have lived in France for the last 8 years or so and am acquainted with the area Jamie is moving to as part of the River Gartempe valley falls within my working area and we have visited the other parts. Dependent on which part of the Gartempe you intend to fish you will catch barbel, especially from the Montmorillon through St. Savin and beyond. Size wise, you'll probably find plenty of 3lb fish with the odd 4lb and topping out around 5lb. This is the same for many rivers in this region in my experience. The post from Lee Williams is interesting as I fish the Vienne regularly and have never seen or heard of anyone catching barbel over 5kg. I hope that it is true, but if the figures had been quoted in lbs and not Kgs I would have agreed whole heartedly.
The Gartempe is I believe a tributary of the Creuse which is not a noted large barbel river. Salmon are being re-introduced and I have seen parr in the Gartemp near to St Ouen sur Gartempe.
The River Vienne isn't too far away and there are places you can expect to catch barbel above the usual 3lb stamp. The Vienne in places has carp to mid-forties, but the barbel in my experience top out just over 9lb. In France a 4Kg or roughly 9lb, barbel is regarded as a true specimen and not many anglers have seen fish over 6lb. I saw a newspaper article of someone catching a 3,7Kg fish from a Vienne tributary so rare are these captures.
The Charente is another of my local rivers. Both the Charente and Vienne are roughly the same length of the Severn albeit with larger catchment areas. Whereas the Vienne is a freestone, rocky river akin to the Wye, the Charente is for much of its length a chalk stream. From Angouleme downstream it is navigable and so has locks and weirs plus lots of riverside access via the 'Chemin Halage' or towpath.
I have had scraper 9lb barbel from both rivers fishing deeper channels with particle baits. French rarely fish for barbel so mostly the fish outside the 'carpe de nuit' areas haven't seen baits. Donkey chokers and the latest flavoured boilies are wasted on them. Better with boiled whole maize grains or small 6mm or so pellets. I do better with squid & krill than halibut. Luncheon meat and home made pork meat balls are readily taken by carp, chub and smaller barbel, but all the heaviest fish I have caught have been on maize or 6mm SK30 pellets. The heavier you feed the more bream you will catch on the Charente. Not so applicable on the Vienne as bream are less common. If you fish luncheon meat or large meat baits in September through to November you are asking for trouble. The large catfish are most active in the period and will trash your barbel gear.
If you are looking for large barbel then the rivers north of the Loire catchment system and in the east of the country will give you the best chance of avoiding the hoards of 3lb shoal fish. The Seine system, the Aine and Oise and the Rhone system are probably the best bets. I have heard of monster barbel being seen in the rivers of the south-west; Lot, Dordogne, Tarn for example, but despite a lot of research and many questions to fellow French barbel addicts I have not seen the proof or photos or catch reports to substantiate the rumours.
Anyone coming to France and intending to fish away from the 'Parcourse de Peche' zones I would advise bringing a latex landing net and long handle to give you a fighting chance in areas where the banks are high and overgrown.
Hope that helps.