ONe board size usually has 2 sail sizes that work best. A 6m with the 133, would feel, not so good. The second sail size should always be the largest for your next board down. Simply put its easier to use another board to increase wind range, than rigg up another sail. so 133/105 is a good combo.
You really have to decide, in what conditions you are looking to get the most out of your gear. At 70kg I would have this combo F122/F93. Sail 8m V8, 6.5v8 & perhaps a 5.4/5.8. Where 6.5 is great on the 122, and superb on the F93 (I should know as I had one). With good technique and a larger slalom fin (46cm) , the 122/8m will still get you going in 10 knots of wind or less @ 70kg, even in a lake
Hope this helps