Overiew / Experience: We just spent 10 days hiking the Tour du Mont Blanc (late August and early September) and it was hard but fabulous. It's a 107 mile hike around Mt. Blanc via France, Italy and Switzerland staying in small towns and refugios along the way. We self organized our trip which worked out beautifully. We booked mostly private rooms along the way in January of 2017 and so were able to get them (private rooms are in limited supply in refugios). It's easy to do it yourself though many Americans were part of a tour group (REI, Mac Adventures and others). The hike itself was so gratifying, peaceful, beautiful and enjoyable. It was more urban than I anticipated with sometimes walking on pavement or just behind people's homes, but a good amount was also in the mountains. Favorite parts included the Italian alps and Lac Blanc near Chamonix (our last day). The tough part was the 13 miles of walking in a down pour.
Fitness Level: We are relatively fit and in our mid 40s. The hike involves daily ascents of 1500-3500 feet with similar descents so you definitely got your work out in every day. For a frame of reference, I'm 48yo female with a BMI 27. I run ~3x week with 6 miles my longest run. The other days I walk the dogs ~3 miles. With my fitness level it was hard but doable. We were probably faster than most hikers, especially those in group tours. The pace of most tour groups was pretty slow so I don't think one would need to be as active as I am to complete the hike. It might be more painful though because some of those ascents were pretty long (2+ hours) and steep.
Gear: We packed pretty light. We each had 15lb-18lb packs. Mine was a 40L (husband 44L) pack. It was 4-5lb heavier with 2 liters of water and lunch added daily. My pack wasn't full - I could probably do a 32-35L next time; husband could do 40L (he's 6'3"). Key clothes included 2 short sleeve wool t-shirts (they don't hold smell) and 2 long sleeve wool t-shirts. (I love Ibex brand wool.) I had a pair of 1 wool tights (sleeping), 1 short (hiking when warm), 1 pairs stretchy tights (hiking when rainy/cold) and 1 long lightweight pant (after shower/evening, break day attire). We brought gortex rain coat, puffer, rain pants, ball cap and thick wool hat and gloves. I wore it ALL. The first 5 days were hot (shorts), the last half was rainy and cool (tights) and in some places downright cold (my light gloves were insufficient). Layering was key as was having great hiking boots/trail runners (I had trail runners that worked great).
Anyway, if it's a hike that's interested you just know it's doable with a reasonable fitness level and you can plan it yourself if you like, even if you don't speak very much French. For us, it's made us excited about doing other long walks in France where we don't need camping gear and can have a good hot meal and a bottle of wine at the end of a long walking day. Not sure where next....maybe Pyrenees, Brittany or the GR 5 to Nice.