In my workbench build I first used 2x10s ripped down the middle and I can confirm that they will likely want to bow on you. A few of mine pinched the riving knife badly enough to need wedging. And then they continued to bow after cutting making for a pretty uneven glueup. I scrapped those top sections and used 2x6s instead which made the glueup a lot more uneventful. And I did special order "#1" wood so it was quite straight with each piece only having a few knots.