I own a VX II and will never own anything less inquality. I had the oppurtunity to compare a 3-9x40 vs a 3.5-10x50 and i didn't notice much differance in clarity at dark. how you intend to use it would be a major factor in buying one. if you want a light weight good clear scope a 40 would probably satisfy your needs. But if you want the maximum for potetinal in clarity and light transmission the 50 is the way to go. correct me if i'm wrong but 50 had a bigger F.O.V. ?