RE: 40mm scope versus 50mm...
Kbeaner...I called Leupold a few years back and asked the difference between 40 and 50 mm objectives...The 50 lets in about 3% more light if the lenses have the same coatings etc...
Now, what does this mean to us deer hunters?? I bought a VX-II 3x9x40 and my brother (the one always wanting bigger/better...) bought the
VX-III 3.5x10x50 for his .280...
Let me make a couple of points as I have hunted and killed deer with his setup...
1) The 50mm affects your cheek weld on the stock, not as bad as see through mounts, but enough that when I shoulder his gun I have to move my face to look through the scope...
2) I can tell no difference in how "late" you can see to shoot deer...In other words, in a quality scope a 40 mm is plenty bright to shoot even as much as 15-20 minutes after legal shooting time is over....This in itself makes a 50 mm a mute point to me...
3) As you get older your pupils will not dialate as well as when you are younger....Guess what, that little bit of extra light the 50 mm gives ain't going to help if your eyes can't use it....
The biggest improvement I have made to my two Leouplds on my deer rifles were to return to Leupold and have the Heavy Duplex reticle installed...The crosshairs are what fade in low light, more so than the deer.
One other point...The Leupolds I have are the older VX-IIs...The current VX-I has the same glass as I have...The new VX-II and VX-IIIs let in even more light than mine would, but mine is plenty bright...I'd go with the 40mm...
Hope this helps...