I've been following this question and I will add my 2 cents based on my experience with hundreds of hours on different thermals, both 320 and 640 core units.
I agree with Gman, get a scanner, and a scope, if you can afford it. For a scanner I prefer a wider wield of view than a high native magnification. I will say that a 320 core scanner is plenty good enough for the area that I hunt, but I did upgrade to a 640 this year. The new 640 does not show a thing that the 320 did not show, just better detail. I am only using it to spot a heat source, when I do I immediately switch to the rifle. And I agree with what he said about FOV. More is better at night.
I also agree with Old Cat, for the rifle you will want a 640 core. That is what you will be looking through and making the ID when you pull the trigger, not the scanner. Down here in the East a 50mm lens would not be necessary but the native magnification would be nice if you can afford it.
I won't recommend one brand over the other, that is a personal choice.