Re: Madison River this September...
I just returned from 8 days in Montana that included a full day on the Madison near Ennis. We caught browns and one rainbow, all 16" to 19", and lost a couple much larger; and we caught one rainbow of 18"--most on an X-Caddis. We often fished two dries at once: an X-Caddis and a Parachute Adams, size 16 or 14 and with the second fly tied as if a dropper about 18-24" off the bend of the first fly. The hoppers or hoppers with a dropper just were not producing as we expected they would.
My 8'6" 5wt. does fine but my friend's 9' 6wt. handles the brutal winds better. I doubt that your 7' 5wt. cane will be enough rod.
The Madison is an amazing stream and you will enjoy the experience. It also is a long stream that is very different near the park (where your shorter rod will work) from what it becomes as it gets down around Ennis. I could spend a lifetime on that one river and not grow weary of it. But then, Montana has an endless supply of interesting streams.