If you’re just using your 7.75 to work on flat and maybe some manuals 129s should be fine, but if you plan on skating curbs, ledges, or rails then 139s should be highly looked into. 129s are great for flat and flip tricks and pretty much everything else BUT grinding; every time I would skate a curb or ledge on 129s it just felt so unstable and wobbly and squirrelly when I was on it, so I pretty much use my 7.75 strictly for messing around on techy flatground stuff now whenever I get the urge to do so and have pretty much moved back to my wider setup for whenever I’m skating anything else.