Re: should i go 34mm?
Scope tube diameter is one of the last thing I would select and I would select it based on application. For a rifle needing to conserve weight you probably do not want a 34 or 35mm tube, but if your are setting up a heavy (or mid-heavy) barrel rifle for precision work at distance you are already focused on higher magnification and a bit more weight should not be a problem. I have a 35mm tube USO SN-3 (3.2-17x)on my heavy barrel 308 and it is wonderful! I am using 35mm Badger Ord. rings on a Badger 20MOA slope base.
But lets say you are making up a lightweight tackdriver and are using a heavily fluted 20" barrel from a good manufaturer on a short action receiver with a Manners light or McMillan Edge stock, if you stick with a 3-10 or 4-14 Leupold VX3 (or Zeiss Conquest) with a 1" tube and lightweight mounts you can have an accurate rifle and keep it under 10 pounds. My 308 above is 12.5 pounds with the USO scope and fluted Kreiger barrel, like I said, I love it but which one would you choose to carry on a long hike?
Now if you have to have all the features of a good tactical scope then you will have to get a bigger, heavier scope with a 30mm or bigger tube. It is your choice, just make it based on YOUR actual needs.