Yea I considered Christopher Schwarz comment about 4×4 but his main concerned seemed to be knots and cut. If you look at my pictures you can see that I rooted around the pile (for quite awhile) to find almost all quarter sawn or rift sawn wood. I also let the wood sit in my shop for at least a month before planing the sides and gluing together. The top has been very stable for the last month it has been glued together.
I wish you the best of luck with your next bench (I think the basic frame is fun just hate the price of the hardware).