You can always turn the 4-16 down. I had a shot a few years ago where I had to negotiate a small sapling between me and the deer. Without the added magnification I probably couldn't have made the shot.

My favorite hunting scope is a 2-7 but my hunting is limited to 200 yards.

QUALITY TRUMPS MAGNIFICATION EVERY TIME

Yep, you'll never notice the added weight of a 4-16 scope, but you'll sure notice the difference between 9x and 16x. I would definitely get the 4-14x40 or 4-16x40

For reference, the weight difference on a Nikon 3-9x and 4.5-14x is about 1.5 oz according to their website. The 4-16x42 weighs about 5 oz more.

If you are still hunting (sneaking around making a little noise), then I would suggest a 2x7x32. If you are stand hunting, i would suggest a 3x9x40. If you are bean field hunting I would suggest a 4x12x40 or 4x16x 40. If you are subject to do all three, I would suggest the 3x9x40. If you are riding around in a jeep then by all means go bigger.

Regardless of the scope you buy, keep it on the lowest power setting until you have your quarry in the crosshairs then crank it up to higher power settings. Hope this information helps.

I think that with most things there is more than one right way to do it. For myself better glass trumps more magnification. If I have $400.00 to spend on a scope then I will buy a 3-9 or 3.5-10 with a 40MM objective as opposed to a 4-12 or 4-16x50 because I want better glass. Better low light performance is more important than magnification. I don't expect what works for me to work for anyone else.

At that price point you're not going to see significant differences, IMHO.

how much of difference does a 30 mm tube make over a 1 inch?

It is to give room for the elevation travel for shooting long range. It also makes a slightly stronger scope tube.

If you're only pushing to 400 yards, you'll be fine with 1" tube or 30mm tube. All of mine are 30mm, bit because for me to get the features I want in a scope, those scopes come in 30 mm or even 34 mm tubes. I also use all of that travel, but that's to get to 1000 yards or more.

I hit a sapling once at 110 yds, Mulie turned and I put one thru it's neck, 4x33mm.
Killed alot of game w/fixed scopes from 2.5-6x. Also used 24x and under variables.

Scope choice is subjective. I'd be content with a 6x or variable topping at 7-8x, I like low mounting and light weight. A turret or reticle can handle distance. A 10-12x is the highest I'd want if carrying a rifle alot, but a 14-16x is not excessive if you are in a box blind and have a rock solid rest, they double for varmints. Took a yote at 175 in the face as he was full frontal, on about 12-14x, and a bobcat raking going away, same distance and power, used the 6x on a headshot at dusk on a deer. 45 yds. All w/a Ruger #1 in 6BR and 6-24x Elite SF 40mm. Same gun, but AO model Elite dropped a deer at 400 yds. Both Mil dot scopes, I simply used the proper dot for reference.

For a field rifle, personally 14-16 is max but the little SF model above was compact so it was much better aesthetically than the AO. Weight and bulk matter to me, as does quality glass.

Whatever you use, if you practice often, you will learn how to hit vitals and be very effective. No substitute for range time.