3top, I have done some sling / long line with Al III but 316B only (with SA319 MGB installed) and I don't know much about 319 models in load lifting. The only thing I can say is that the performances graphs in RFM are fairly accurate, and we usualy have no surprise if we plan our flight with them.
Another thing, Astazou engines are more sensitive than the old artouste III and a good compressor wash is always a good thing to do before heavy loads liftings (same with rotor blades)
But these Alouette III are really a pleasure to operate and fly, I always had the feeling they like to fly as they like their drivers.