Depends on your eyes. If you see details well, the lower power is more than enough. However, if small things get fuzzy, you might find the higher power really helps at long range.
I should know. I had a Leopold 3-9 on a 30-06. I found that I just couldn't quite get the long range accuracy I wanted. I switched to a 4-12 and it helped a lot. Getting old is a bitch.
