I had originally planned to go with the 35 Whelen. But the rifle builder said he had a 35 Whelen Imp reamer also, and that would give me better headspacing, and the cases would stretch less, plus a little more velocity. So that's what I went with. I took that rifle to Newfoundland Sept 2001, for moose and caribou. 10 days after 9/11, and I was amazed we just breezed through the border, with declared guns, both ways.
Although some load data is out there, good comprehensive load data is scarce, so I was on my own. I was advised by the builder to start at the max loadings for the standard Whelen, and work up. So that's what I did. My settled load was getting over 2700 fps, and over 4000 ft lbs, with a 250 gr Speer Hotcore bullet. I have a detachable muzzle brake on the rifle. DRT on both animals. I don't know how much the gain was over the plain old 35 Whelen, as I don't have a before and after measurement. I know one of the writers for Handloader magazine claims the 35 Whelen Imp is the most worthless wildcat. I tend to disagree. After the hunt, my muzzle brake was removed, and the Whelen Imp is now a cast bullet rifle. Ringing the gongs at 100 yards is it's repurposed use.
If there are any faults with the Imp cartridges, it's in feeding. The sharp shoulder of the Imp case, in some rifles can cause issues. My rifle has a fiberglass stock with a deep magazine well. It holds 7 rounds. If I put more the 5 rounds in the magazine, I often have troubles with the case shoulder hanging up. 5 rounds or less it works fine.
I tried to post a picture, but the size was too large for the system to handle. I will try my other camera later.