Going to 149's was the best decision I made with my setup. ? I was tired of skating my 8.125's in the local wooden bowl or any bowls for that matter.I didn't want a 8.25 with 139's cause I felt like that defeated the purpose. ? At first I kept my 8.125 board with the 139's for anything else other than the bowl I was skating. I quickly realized the bigger wider board was way more to fun ride.
To be more technical, if you are riding 149's with a board smaller than an 8.25 than your weight transfer isn't getting out and over the axles and making it harder to turn. Rather than having a board that is just as wide if not wider than your trucks, you can turn them much easier cause your weight will be concentrated on the edge of the board, which in turn will be on or outside of the truck.
This is just me spit-balling at this point but I feel like with a wider board you have more leverage with your flip tricks. Say you have a 7.75 and you kickflip. Your flick is going to have to be more downward rather than outward, cause there is less surface for your foot to catch the board, making your board flip really fast. ? While if you have a bigger board, you can give a nice stylish flick out to the side,and that extra width of the board will help give you a "flick" rather than pushing down on it. I compare it to screwing around on just an old deck on carpet to having a full set up. This is just me though, and I'm curious if this makes sense to anybody else.