I've not done testing with the different twist rates, but I do have a .35 Whelen AI with a 40 degrees shoulder. You can expect about 100-150 fps over the data for the standard Whelen you see in the various manuals. The one I have is on a Parker-Hale (commercial M98) action with a 25" Douglas barrel. It shoots everything from 180's to 250's very well. You can expect about 28-2900fps with the 200's, the 180's will go 3000fps if you develop loads carefully. You can expect 2600-2650+ with the 250's. These velocities are from the above mentioned 25" barrel, so take that into account if you're planning on something signifigantly shorter. I haven't had the chance to work with this rifle all that much, but I've taken a whitetail doe and a midsized black bear with it. I will say that it performed admirably. More so than the standard Whelen? I can't say. The 180gr X-bullet shoots fairly flat and makes short work of deer.