For ten years, I flew a C-185 on late model PK straight 3500 floats, based at the Fairbanks float pond. That airplane was replaced (against my recommendation) by a U-206F, equipped with an IO-550 and Wipline 4000 straight floats. Both the 185 and the 206 were RSTOL equipped.
It took me a while to get the hang of the Wip 4000 floats (and they are still not my favorites), but once I did, I found that 206 would get out of the water at a MTOW of 3800 pounds at almost exactly the same spot the 185 launched at 3350 MTOW.
There's no doubt the extra oomph of that IO-550 made a big difference, but that's also a substantial weight difference.
We also had a 550 equipped F model 206 on Wipline 3450 amphib floats. Also approved at 3800 MTOW, and that airplane was a really good performer off the water. It had been thoroughly stripped of non essentials to lighten it up. It also had 125 gallons max fuel.
I'd have loved to have put a set of 3450 straight floats on the 206 with the 4000s. Those floats were water lovers, till I figured out that if you stomped hard on the rudder once the airplane was running clean on the step you'd actually turn the airplane somewhat sideways in the water, and it'd pop right out and fly.
A great way to make check airmen crap their pants, by the way.
I learned to love that 206, in any case. A real workhorse, and I took it everyplace I took the 185, with bigger loads.
MTV