I've ran a few 1.2" shank barrels with the Tikka tenon, no issues. Doesn't look great as the nose of action is slightly tapering diameter to the face, and then the shank is slightly bigger. I'm not home at the moment to take pics. If I were to do a non magnum 7mm build on a Tikka, I'd no doubt go with a 284win utilizing lapua brass. Run a long action bolt stop and oem Tikka 30-06 or mountain tactical magazines. I'm just not a big fan of magnum case heads on the 1" tenon threads, although plenty of folks do it, myself included, but have sold most them off. 284win offers a bit more horsepower. You could also do a straight 7-08ai since you'll be fire forming the 7saw as well. Magazine length is no problem on the Tikka as they're all technically a long action receiver, bolt stop and magazine selection be your limiting factors on cartridge overall length. I recently built my GF a hunting rifle on a 65cm Tikka donor that she'd been using for 2 years prior. Now that the hunting bug bit her, she wants to chase elk. I wanted a bit more case capacity. I really wanted to go 284win, but since I'm already tooled up for 65prc with dies and brass. Went that route(smith easily opened bolt face on his mill). The rifle shoots extremely well with 140hyb at 2950-2980 with H1000, N565 and retumbo from a 24" carbon barrel. I'd say the PRC cases with the 535 chamber diameter are a better choice over a Saum/wsm with the 555 chamber base on the 1" tenon diameter. Then again I'm probably over thinking it like everything else! Best of luck!