Own any LPVOs? There is a noticeable difference between the FFP 1-6x vs the 1x8 Credo (yes, I own both).
The high end 1-8/10 FFP are damn incredible vs the traditional 1-4/6. The latest version of the upper end 1-10x's are worth considering.
I like the 34 mm tube as I feel that it gathers more light even - maybe its just maybe my mind. But when I have both rifles at the same time/location and do a side to side - the 1-8x has the "damn" factor.
Parallax on some FFPs - a side focus can help with the image at full magnification-
yards has nothing to do with it.
Btw, I had the CREDO 2-10x 36 FFP scope and the image was soft at max mag. Im not the only one who noticed that a side focus would have help -
Forgive me in advance for repeating this -
nothing to do with yards but magnification of the specific design.
For what it worth - this my experience with a few FFP's 2x-10 range on 308/30.06/338 with and w/o side focus and multiple (1-4/6/8) LPVO's on 556. My favorite 2/2.5-10x that own are the Vudu 2.5-10 FFP and Viper 2.5-10x32 FFP GEN 1 with a side focus at 18oz (both are discontinued).
Caveat Emptor - YMMV
Peace