If you intend to get a 444 Marlin, the Encore frame will be your best bet. Yes the G-2 Contender frame can handle the 444 Marlin, but no sense pushing the envelope.
As for barrel length I would recommend a 15" barrel in mid varmit contour with a slight taper so the barrel ends up at 8/10".
Encore barrels start with a 1" tube and can be made to any contour. The extra weight of the heavier barrel with take some of the recoil and make it a pleasure to shoot. You may even want to consider a muzzle break as a extra feature. Recoil will definitely be reduced.