Quit considering and just do it... 35 Whelen/AI is my favorite big game rifle bar none. Elk, mule deer, whitetails. It's a 400 yd gun with the 200 TTSX. A good 3-9X or similar will be great, my opinion is more X's in a scope has been an overrated and unnecessarily theme. If a guy needs more than that range, stop shooting at big game and start hunting it, lol.
I posted earlier in this thread, however can't recommend the cartridge enough in the rifle of your choice. Modern powders push a 200 gr TTSX over 3000 fps safely, 225 gr over 2900 fps and 250 gr over 2700 fps in published data, not some figment posted for pie in the sky velocity.