Owning a Lasernut U4, and being on the FB page for the LN U4, I can tell you we ALL hate the stock rims hex. You can also see that on some YT videos. The BF tires are great, so much so I removed them from the rims and put them on a better rim for better hex support. The shallow and soft hexes will not last on the stock LN rims. It does not last on the LN for serious bashing, so the Big Rock is a true basher just do not see it lasting.
I did use the PL SC tires on my Big Rock for a short item...so it was a bit taller also. It traction rolled too much. As soon as I turned hard, it rolled over. Stock tires are good, and the PL Badlands MX 2.8 are the best for bashing....size and weight!
Please take it slow.... The Big Rock is a great rig. The motor and ESC will work great for the stock tires or PL Badland MX 2.8". You will overheat the rig with the wrong tires or specific changes if you do not balance out correctly for this rig.
What is your goal? What is it you want to do? Would a 4S rig be better for you or a Kraton 6S rig, etc? You can quickly get into a money pit here or keep it as it is and get another rig to suit your needs vs. the money it takes to shoehorn the 3S rig here...you could have bought a better rig.
Just pace yourself and determine what it is you are trying to do.